Suppose that a and b are positive real numbers, and let

f(x) = a/b*x if x <= -4

f(x) = abx^2 if x > 4

If f(-4) = -60/7 and f(4) = 3120, what is a + b?

In your statement of the problem, f(4) is undefined.

Gino is right,

You have copied the question incorrectly.