(1 point) A company estimates that it will sell NV(x) units of a product after spending x thousand dollars on advertising, as given by N(x) = -4x' + 240x - 3300x + 15000, 10 S x 5 40. (A) Use interval notation to indicate when the rate of change of sales /'(x) is increasing. Note: When using interval notation in WeBWork, remember that: You use 'I' for co and "-l' for -co, and 'U' for the union symbol. If you have extra boxes, fill each in with an 'x". N' (x) increasing: (B) Use interval notation to indicate when the rate of change of sales N' (x) is decreasing. N' (x) decreasing: (C) Find the average of the x values of all inflection points of N(x). Note: If there are no inflection points, enter -1000. Average of inflection points = (D) Find the maximum rate of change of sales. Maximum rate of change of sales = (1 point) If the figure below is the graph of the derivative f', answer the following: Where do the points of inflection of f occur? On which interval(s) is f concave down? (1 point) Use the given graph of the function f to answer the following questions. Note that the function's domain is the interval (0, 8). 1. List the open interval(s) on which f is concave upward. If there is more than one such interval, write them as a comma-separated list. Answer (in interval notation): 2. List the open interval(s) on which f is concave downward. If there is more than one such interval, write them as a comma-separated list. Answer (in interval notation) 3. List the points of inflection. Write your answers as points in the form (x, y). Answer (separate by commas)