A poll was taken of 100 students at a commuter campus to find out how they got to campus. The results are below.

Question

57 said they drove alone.
29 rode in a carpool.
30 rode public transportation.
6 used both carpools and public transportation.
9 used both a carpool and sometimes their own cars.
10 used buses as well as their own cars.
4 used all three methods.
Use the figure to answer the question in the problem.

How many are using all three (Region VII)?
students