Explanation:
Set up a systems of equations (x = kids, y = adults)
3x+9y=75 --> 15x+45y=375
8x+5y=67 --> 72x+45y=603
Subtract the two equations
57x = 228
x = 4
A KID'S TICKET IS $4
Plug that in for x
4(3)+9y=75
12+9y=75
9y=63
y=7
AN ADULT'S TICKET IS $7