Let y = f(k, l) = 15k^1/5 l^2/5 denote the number of units produced when k units of capital and l units of labor are used as inputs. (a)- find an expression for f(k + 1, 32) − f(k, 32) and give an economic interpretation. (b)-there is a constant r such that f(3k, 3l) = 3rf(k, l). find r.