Your first two answers are correct.
For the last answer, take your middle answer and divide it by h.
-h/h = -1
This formula, ( f(x+h) - f(x) ) / h, is really just a different form of the slope formula, m = (y2- y1)/(x2 - x1). You’re really just finding the slope, which you might see in the original function from the f(x) = mx+b form.
