A manufacturer of athletic footwear finds that the sales of their ZipStride brand running shoes is a function f(p) of the selling price p (in dollars) for a pair of shoes. Suppose that f (120) = 9000 pairs of shoes and f '(120) = 60 pairs of shoes per dollar. The revenue that the manufacturer will receive for selling f(p) pairs of shoes at p dollars per pair is R(p) = p f(p). Find R' (120). What impact would a small increase in price have on the manufacturer's revenue?