A theater seats 500 people. Each adult ticket, a, sells for $7.50, and each student ticket, s, for $4.50. On a Friday evening, every seat was filled, and the theater made $3,150 in ticket sales. Which system of equations could be used to find the number of adult and student tickets sold on Friday evening?
a + s = 3,150
7.5a + 4.5s = 3,150
a + s = 500
7.5a + 4.5s = 3,150
a + s = 3,150
7.5s + 4.5a = 500
a + s = 500
7.5a + 4.5s = 500
