A poll was taken of 100 students at a commuter campus to find out how they got to campus. The results were as follows:

33 said they drove alone.
31 rode in a carpool.
37 rode public transportation.
9 used both carpools and public transportation.
6 used both a carpool and sometimes their own cars.
6 used buses as well as their own cars.
4 used all three methods

What is the question?

To find out how many students used only their own cars to get to campus, we need to break down the given information step by step.

First, there were 33 students who said they drove alone.

Next, we have information about students who used multiple methods of transportation. We're told that 6 students used both a carpool and sometimes their own cars, and 6 students used buses as well as their own cars. This means that we need to subtract these 12 students from the initial count of 33 who drove alone.

33 - 12 = 21

So, 21 students used only their own cars to get to campus.

Therefore, the answer to the question is that 21 students used only their own cars.