Sync Block In Java - Servlet

Modify the program in Assign4 to synchronize access to the instance variable, balance. Save the program as SyncBank.java. Because balance is a double and not an object, it cannot be used as the monitor. Use synchronized methods or synchronized blocks of code as appropriate. Simultaneously test two threads as was done in Assign4. Because the threads can complete too quickly to determine if they are interfering with each other, delay the adding of a deposit by inserting the following code within the synchronized block or method:

try {
Thread.currentThread().sleep(10000); //sleep for milliseconds
}
catch(InterruptedException e) {
}

My code attempt so far:

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*;
import java.net.*;
import java.text.DecimalFormat;
public class SyncBank extends HttpServlet //throws ServletException, IOException

[Code] .....