the format of your question screams "copy and paste" from your homework;
That's a little frowned upon here, so lets do it right:
can you show us the query you've created so far, and explain what doesn't work, or where you are stuck?
we would love to help you master the problem, rather than do it for you;
you'll suffer later if you don't grasp this concept yourself, because later homework will certain build on top of the basics like this.
--help us help you! If you post a question, make sure you include a CREATE TABLE... statement and INSERT INTO... statement into that table to give the volunteers here representative data. with your description of the problem, we can provide a tested, verifiable solution to your question! asking the question the right way gets you a tested answer the fastest way possible!