We have two variables the amount of full price tickets, we call x, and the discounted tickets, we call y.
From the problem, we know the total amount of tickets, 576=x+y, and the total money for the sales $5769, and the prices fro full ticket is $12.75 and for discounted ticket is $7.50.
So the equations are:
Solving the above system of equations:
So, were sold 300 dicounted senior/student tickets