The Acting Conservatory is running a concession stand at a showcase. They are selling a bag of popcorn for $1.50 each and Skittles for $0.50. At the end of the night, they made a total of $78.50. They sold a total of 87 bags of popcorn and Skittles combined. Write a system of equations to best represent the constraints of the situation. Be sure to define all your variables. Do not solve the system--just represent it algebraically.