+3x2-24x + 24. Let f(x)=x+3x (a) Use the definition of a derivative or the derivative rules to find f'(x) = (b) Use the definition of a derivative or the derivative rules to find f"(x) = For the next parts of the problem, used closed interval notation to enter your answers: (c) On what interval is f increasing (or more specifically, non-decreasing)? interval of increasing = (d) On what interval is f decreasing (or more specifically, non-increasing)? interval of decreasing = (e) On what interval is f concave downward (include the endpoints in the interval)? interval of downward concavity (f) On what interval is f concave upward (include the endpoints in the interval)? interval of upward concavity =