NWAU 9 10 11 12 (a) Find the intervals where f is concave upward and the intervals where f is concave downward. (Enter your answers using interval notation.) concave upward (0,2), ( 4,6), (7,9), (9,12) (0, 2), (4, 6), (7, 9), (9, 12) concave downward (2,4), (6,7) (2, 4), (6, 7) (b) Find the inflection points of f. (Order your answers from smallest to largest x, then from smallest to largest y. If an answer does not exist, enter DNE.) (x, y ) = ( x, y ) = ( x, y ) = ( x, y ) = ( Effect of Advertising on Hotel Revenue The total annual revenue R of a certain resort hotel is related to the amount of money x the hotel spends on advertising its services by the function R(x) = -0.004x + 1.5x2+ 5x + 9,000 (0 S x S 400) where both R and x are measured in thousands of dollars. (a) Find the interval where the graph of R is concave upward. (Enter your answer using interval notation.) Find the interval where the graph of R is concave downward. (Enter your answer using interval notation.) What is the inflection point of the graph of R? (x, R(X)) =(