MS. Sue can you explain me the problem please

What part don't you understand?

How long did Michelle sleep if she went to bed at 9:40 PM and got up at 7:20 AM.

Math - Ms. Sue, Tuesday, February 7, 2012 at 10:08pm

11:60 - 9:40 = 2:20

2:20 + 7:20 = ?