Keith will run at most 39 miles this week. So far, he has run 21 miles. What are the possible numbers of additional miles he will run?

Pls , the question is in the picture!

Let f(x) = 3 − x . find the average rate of change of f(x) from x = a to x = a + h and simplify your answer so that no single factor of h is left in the denominator.

Can someone me out here and the tell me the greatest common factor