Determine the average cost function C(x) = - -. To find where the average cost is smallest, first calculate C (x), the derivative of the average cost function. Then X use a graphing calculator to find where the derivative is 0. Check your work by finding the minimum from the graph of the function C(x). C(x) = 3 + 4x - 4x + 20 Determine the average cost function. C(x) = Calculate C'(x). C'(x) = C'(x) =0 when x =_ (Type an integer or decimal rounded to three decimal places as needed.)