Okay, well with the information given, you can not come to an answer. Is there something that shows all of the students who were in the survey?
Edit: Okay so there are 520 students in total.
We can say that the graph is equal to 520/520
However, we are trying to find how many of the 520 people voted for james. We know that James received 15% of the votes.
Now, we can find 15% of 520 by taking 15/100 times 520. The answer is 78.