Question

A poll was taken of 100 students at a commuter campus to find out how they got to campus. The results are below. How many are not using any of the three?
32 said they drove alone.
34 rode in a carpool.
31 rode public transportation.
7 used both carpools and public transportation.
8 used both a carpool and sometimes their own cars.
9 used buses as well as their own cars.
5 used all three methods.