Since 111 is greater than 33, I will assume that you meant 11 votes for a candidate. Also, assuming that each student can vote only once, the answer would be
11/33 x 100=33.333333...
About 33.333 of the voters voted for candidate a.
Hope you could get an idea from here.
Doubt clarification - use comment section.
C is your answer since it is the only one without any exponents