Answer:
750
Step-by-step explanation:
I'm gonna make my best effort here... (it's been a long hecking time since SAT math last year :P)
Set both equation equal:
5x = -15x + 3000
20x = 3000
x = 150
Plug into any equation because both are equal anyway:
y = 5x
y = 5(150)
y = 750
(a, b) --> (x, y)
The point is (150, 750) and b = 750