14. I need help with this problem, please.

The temperature in an industrial pasteurization tank is ((x) = x - 7x + 106 degrees centigrade after x minutes (for OS X 5 14). (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--- v at a rate of degrees per minute after 2 minutes. (c) Use your answer to part (a) to find the instantaneous rate of change after 8 minutes. The temperature is ---Select--- > at a rate of degrees per minute after 8 minutes