[-15 Points] DETAILS BERRAP The temperature in an industrial pasteurization tank is f(x) = x- 9x+119 degrees centigrade after x minutes (for 0 x 13). (a) Find f'(x) by using the definition of the derivative. f'(x) = (b) Use your answer to part (a) to find the instantaneous rate of change of the temperature after 2 minutes. Be sure to interpret the sign of your answer. The temperature is --Select--- Bat a rate of degrees per minute after 2 minutes. (c) Use your answer to part (a) to find the instantaneous rate of change after 6 minutes. The temperature is --Select--- B at a rate of degrees per minute after 6 minutes.