A poll was taken of 100 students at a commuter campus to find out how they got to campus. The results were as follows:
34 said they drove alone.
25 rode in a carpool.
28 rode public transportation.
4 used both carpools and public transportation.
7 used both a carpool and sometimes their own cars.
4 used buses as well as their own cars.
3 used all three methods.
How many used none of the above-mentioned means of transportation?