Consider the following function. f(x) (8 x)(x+1) (a) Find the critical numbers of f. (Enter your answers as a comma-separated list.) x = 5 (b) Find the open intervals on which the function is increasing or decreasing. (Enter your answers using interval notation. If an answer does not exist, enter DNE.) increasing decreasing (-1,5) (c) Apply the First Derivative Test to identify the relative extremum. (If an answer does not exist, enter DNE.) relative maximum (x, y) = 5,108 relative minimum (x, y) = -1,0