(Questiоn 6) 12 pоints (а) On whаt intervаls is f increasing ? (Enter yоur answer using interval notation.) (b) On what intervals is f decreasing ? (Enter your answer using interval notation.) (c) At what value(s) of x does f have a local maximum ? (Enter your answers as a comma-separated list.) (d) On what interval(s) is f concave upward? (Enter your answer using interval notation.)