Consider the following function. A(x) - 18-3x Find the derivative of the function. if x < -3 A'(x)- 3 if x> Find the values of x such that A'(x)=0. (Enter Your answers as a comma-separated list. If an answer does not exist, enter DNE.) XM Find the values of x in the domain of A such that A'(x) does not exist. (Enter your answers as a comma-separated list. If an answer does not exist, en X Find the critical numbers of the function. (Enter your answers as a comma-separated list. If an answer does not exist, enter DNE.)