18) f'(x) = (3-x)(8-x) 19) f' (x) = (x-8) e-X Find the open intervals on which the function is increasing and decreasing. Identify the function's local and absolute extreme values, if any, saying where they occur. 20) -6 4 2 .4 Find the largest open interval where the function is changing as requested. x2-9)2