F(x) = 2x^2 - 3x, calculate f(x+h)-f(x) / h

First plug in (x+h) for x in the function.
f(x+h)= 2(x-h)^2-3(x-h) = 2(x^2-2xh+h^2)-3x-3h =
2x^2-4xh+2h^2-3x-3h - 2x^2 +3x =
(-4xh +2h^2-3h)/h
-4x +2h-3