Someone help me with this math problem please!?!?!!? the problem is down below?

Problem: Half of the students who ate lunch at Mesa on Friday brought their lunch and did not buy anything at the cafeteria. Out of the remaining half who bought something, � bought pizza. Out of the pizza bought, � was cheese and � was pepperoni. The remaining 15 pizzas were vegetarian. How many students were eating lunch at Mesa that Friday?