4 y=f'(x) 2 X 2 6 18 -2 (a) On what interval(s) is f increasing? (Enter your answer in interval notation.) On what interval(s) is f decreasing? (Enter your answer in interval notation.) (b) At what value(s) of x does f have a local maximum? (Enter your answers as a comma-separated list.) At what value(s) of x does f have a local minimum? (Enter your answers as a comma-separated list.) x = (c) On what interval(s) is f concave upward? (Enter your answer in interval notation.)