This is not a good example of how to handle threading - to get the required output from two separate threads means that you need to pause one thread until the other has done something, then pause that until the first has done something else.
It's not impossible, or even particularly difficult, but it is a bad example of what to do with threads.
If your homework requires this, then start reading at MSDN:
Threading Tutorial[
^] - if you look at the section "Example 2: Synchronizing two threads: a producer and a consumer" you will find code you can adjust to do what you need.