4. (6 points each) Assume that if we apply u ounces of fertilizer to our garden, we will harvest T' pounds of tomatoes where T' = 200(1 + u - .02u") (a) Find the instantaneous rate of change in 7, with respect to u, when u = 30. (b) Find the total change in 7', with respect to u, if u is increased from 20 to 28. (c) Find the average rate of change in 7', with respect to u, when u is increased from 30 to 32