Each week, John drives to his mother's house. The amount of time required for the trip varies and is normally distributed. On about 16% of trips, it takes him more than 54 minutes to reach his mother's house. On about 2.5% of trips, it takes him less than 33 minutes to reach his mother's house. Which is closest to the mean amount of time required to make the trip?
Full disclosure: I'm studying for a test and this is a question from the practice test and I don't know where to start. I have the answer; I want to know how to get there.