It's a trick question, right? Really, if you can't get this one, you should have a very serious chat with your academic advisor.
30.24 - 1.65 = ?? -- That's one hour
30.24 - 1.65*2 = ?? -- That's two hours
30.24 - 1.65*3 = ?? -- That's three hours
See the pattern. Be the pattern. Free the pattern.