Find the minimum value of the average cost for the given cost function on the given intervals. C(x) =x + 30x + 128 (a) 1Exs 10 (b) 10 sx 20 (a) The minimum value of the average cost over the interval 1 s x= 10 is (Round to the nearest tenth as needed. Do not include the $ symbol in your answer.) (b) The minimum value of the average cost over the interval 10 s x $ 20 is (Round to the nearest tenth as needed. Do not include the $ symbol in your answer.)