Unable to click button "Choose a room" from given url

Code:

import static org.testng.Assert.assertEquals;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.Iterator;
import java.util.List;
import java.util.Set;
import java.util.concurrent.TimeUnit;

import org.openqa.selenium.By;
import org.openqa.selenium.JavascriptExecutor;
import org.openqa.selenium.Keys;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.firefox.FirefoxDriver;
import org.openqa.selenium.support.ui.ExpectedConditions;
import org.openqa.selenium.support.ui.Select;
import org.openqa.selenium.support.ui.WebDriverWait;
import org.testng.Assert;
import org.testng.annotations.AfterMethod;
import org.testng.annotations.BeforeMethod;
import org.testng.annotations.Test;

public class HomePage {

WebDriver driver;

@BeforeMethod
public void setup(){

String value="C:\\Users\\mubeen\\Desktop\\seleniumjars3.8.1\\drivers\\geckodriver.exe";
System.setProperty(FirefoxDriver.SystemProperty.BROWSER_LOGFILE, "null");
System.setProperty("webdriver.gecko.driver", value);
driver = new FirefoxDriver();

driver.manage().timeouts().implicitlyWait(20, TimeUnit.SECONDS);
driver.manage().timeouts().pageLoadTimeout(40, TimeUnit.SECONDS);
driver.manage().window().maximize();
driver.get("http://hotwire.com");
}
/*
@Test(priority=1)
public void getTitle(){
String expectedtitle = "Cheap Hotels, Cars, & Flights | Last Minute Travel Deals | Hotwire";
String title = driver.getTitle();
Assert.assertEquals(expectedtitle, title);
}
*/


@Test
public void homePage() throws InterruptedException, ParseException{
System.out.println("homepage");
driver.findElement(By.xpath("//div[text()='Bundles']")).click();
//int frames= driver.findElements(By.tagName("iframe")).size();
//System.out.println(frames);

driver.findElement(By.xpath("//input[@id='farefinder-package-origin-location-input']")).sendKeys("SFO");
driver.findElement(By.xpath("//input[@id='farefinder-package-origin-location-input']")).sendKeys(Keys.TAB);

// driver.findElement(By.xpath("//*[@id='typeahead-955-6718']/li[1]")).click();
//Select drop = new Select(driver.findElement(By.xpath("//*[@id='typeahead-955-6718']")));
//drop.selectByIndex(1);

Thread.sleep(1000);

driver.findElement(By.xpath("//input[@id='farefinder-package-destination-location-input']")).sendKeys("LAX");
driver.findElement(By.xpath("//input[@id='farefinder-package-destination-location-input']")).sendKeys(Keys.TAB);

Thread.sleep(2000);

Date dt = new Date();
Calendar calendar = Calendar.getInstance();
calendar.setTime(dt);
calendar.add(Calendar.DATE, 1);
dt = calendar.getTime();

String todaysDate = new SimpleDateFormat("MM/dd/yyyy").format(dt);
todaysDate.equals(dt);

//enter tomorrow's date in the Pause field
WebElement tomDate = driver.findElement(By.xpath("//*[@id='farefinder-package-startdate-input']"));
tomDate.clear();
tomDate.sendKeys(todaysDate);


SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy");
Calendar c = Calendar.getInstance();
c.setTime(sdf.parse(todaysDate));
//Number of Days to add
c.add(Calendar.DAY_OF_MONTH, 20);
//Date after adding the days to the given date
String newDate = sdf.format(c.getTime());


WebElement returnDate = driver.findElement(By.xpath("//*[@id='farefinder-package-enddate-input']"));
returnDate.clear();
returnDate.sendKeys(newDate);

driver.findElement(By.xpath("//*[@id='farefinder-package-search-button']")).submit();

List<WebElement> e = driver.findElements(By.xpath("//a[@class='flex-link']"));
System.out.println(e.size());

e.get(0).click();
Thread.sleep(2000);
Set<String> WinIds = driver.getWindowHandles();
Iterator<String> it = WinIds.iterator();

System.out.println(WinIds.size());

String firstpop = it.next();
String secondpop = it.next();
System.out.println(firstpop);
System.out.println(secondpop);

driver.switchTo().window(secondpop);
driver.switchTo().defaultContent();
//System.out.println(WinIds.size());

//driver.findElement(By.xpath("//button[@id='mock-book-button']")).submit();
//WebDriverWait wait = new WebDriverWait(driver, 20);
//wait.until(ExpectedConditions.elementToBeClickable(By.xpath("//button[@id='mock-book-button']"))).click();

/*
WebElement element = driver.findElement(By.xpath("//button[@id='mock-book-button']"));
JavascriptExecutor executor = (JavascriptExecutor)driver;
executor.executeScript("arguments[0].click();", element);
*/
Thread.sleep(3000);
int total1 = driver.findElements(By.tagName("iframe")).size();
System.out.println("total frame1"+"--"+total1);
driver.switchTo().frame(0);
/*
WebDriverWait wait = new WebDriverWait(driver, 20);
wait.until(ExpectedConditions.elementToBeClickable(By.xpath("//button[@id='mock-book-button']"))).click();
*/
driver.findElement(By.xpath("//button[@id='mock-book-button']")).submit();

}

/*
@AfterMethod
public void tearDown(){
driver.quit();
}
*/

}

Error:

[RemoteTestNG] detected TestNG version 6.14.2
Jun 29, 2019 11:32:03 PM org.openqa.selenium.remote.ProtocolHandshake createSession
INFO: Detected dialect: W3C
homepage
5
2
4294967297
4294967358
total frame1--1
FAILED: homePage
org.openqa.selenium.NoSuchElementException: Unable to locate element: //button[@id='mock-book-button']
For documentation on this error, please visit: http://seleniumhq.org/exceptions/no_such_element.html
Build info: version: '3.11.0', revision: 'e59cfb3', time: '2018-03-11T20:26:55.152Z'
System info: host: 'MUBEEN', ip: '169.254.144.87', os.name: 'Windows 10', os.arch: 'amd64', os.version: '10.0', java.version: '1.8.0_101'
Driver info: org.openqa.selenium.firefox.FirefoxDriver
Capabilities {acceptInsecureCerts: true, browserName: firefox, browserVersion: 58.0.2, javascriptEnabled: true, moz:accessibilityChecks: false, moz:headless: false, moz:processID: 69172, moz:profile: C:\Users\mubeen\AppData\Loc..., moz:webdriverClick: true, pageLoadStrategy: normal, platform: XP, platformName: XP, platformVersion: 10.0, rotatable: false, timeouts: {implicit: 0, pageLoad: 300000, script: 30000}}
Session ID: c7fa7b74-6c80-4001-aea5-6a8364600442
*** Element info: {Using=xpath, value=//button[@id='mock-book-button']}
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at org.openqa.selenium.remote.http.W3CHttpResponseCodec.createException(W3CHttpResponseCodec.java:187)
at org.openqa.selenium.remote.http.W3CHttpResponseCodec.decode(W3CHttpResponseCodec.java:122)
at org.openqa.selenium.remote.http.W3CHttpResponseCodec.decode(W3CHttpResponseCodec.java:49)
at org.openqa.selenium.remote.HttpCommandExecutor.execute(HttpCommandExecutor.java:158)
at org.openqa.selenium.remote.service.DriverCommandExecutor.execute(DriverCommandExecutor.java:83)
at org.openqa.selenium.remote.RemoteWebDriver.execute(RemoteWebDriver.java:545)
at org.openqa.selenium.remote.RemoteWebDriver.findElement(RemoteWebDriver.java:319)
at org.openqa.selenium.remote.RemoteWebDriver.findElementByXPath(RemoteWebDriver.java:421)
at org.openqa.selenium.By$ByXPath.findElement(By.java:361)
at org.openqa.selenium.remote.RemoteWebDriver.findElement(RemoteWebDriver.java:311)
at HomePage.homePage(HomePage.java:143)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.testng.internal.MethodInvocationHelper.invokeMethod(MethodInvocationHelper.java:124)
at org.testng.internal.Invoker.invokeMethod(Invoker.java:580)
at org.testng.internal.Invoker.invokeTestMethod(Invoker.java:716)
at org.testng.internal.Invoker.invokeTestMethods(Invoker.java:988)
at org.testng.internal.TestMethodWorker.invokeTestMethods(TestMethodWorker.java:125)
at org.testng.internal.TestMethodWorker.run(TestMethodWorker.java:109)
at org.testng.TestRunner.privateRun(TestRunner.java:648)
at org.testng.TestRunner.run(TestRunner.java:505)
at org.testng.SuiteRunner.runTest(SuiteRunner.java:455)
at org.testng.SuiteRunner.runSequentially(SuiteRunner.java:450)
at org.testng.SuiteRunner.privateRun(SuiteRunner.java:415)
at org.testng.SuiteRunner.run(SuiteRunner.java:364)
at org.testng.SuiteRunnerWorker.runSuite(SuiteRunnerWorker.java:52)
at org.testng.SuiteRunnerWorker.run(SuiteRunnerWorker.java:84)
at org.testng.TestNG.runSuitesSequentially(TestNG.java:1208)
at org.testng.TestNG.runSuitesLocally(TestNG.java:1137)
at org.testng.TestNG.runSuites(TestNG.java:1049)
at org.testng.TestNG.run(TestNG.java:1017)
at org.testng.remote.AbstractRemoteTestNG.run(AbstractRemoteTestNG.java:114)
at org.testng.remote.RemoteTestNG.initAndRun(RemoteTestNG.java:251)
at org.testng.remote.RemoteTestNG.main(RemoteTestNG.java:77)

===============================================
Default test
Tests run: 1, Failures: 1, Skips: 0
===============================================

===============================================
Default suite
Total tests run: 1, Failures: 1, Skips: 0
===============================================

The error is at HomePage.java line number 143.

Also, the code is not able to locate the XPath //button[@id='mock-book-button'] on the page.