Let the number of adult tickets be x
Let the number of child tickets be y
a)Number of tickets sold:
x + y = 800
Dollar value of tickets sold:
5x + 3y = 3600
b) y = 800 - x
5x + 3y = 3600
5x + 3(800 - x) = 3600
5x + 2400 - 3x = 3600
5x - 3x = 3600 - 2400
2x = 1200
x = 1200/2
x = 600
Total number of adult tickets sold = 600