A poll was taken of 100 students at a commuter campus to find out how they got to campus. The results were as follows: 35 said they drove alone. 38 rode in a carpool. 37 rode public transportation. 9 used both carpool and public transportation. 7 used both a carpool and sometimes their own cars. 9 used buses as well as their own cars. 4 used all three methods. How many used none of the above-mentioned means of transportation