80 Based on the following graph of f(x), which one of the following values is a possible value of f(x) dx ? You may assume that f(x) is concave down on the interval [0,80]. Hint: Approximate the area of the shaded region using a rectangle and a triangle. 20 15 10 5 X 80 O 880 1600 O 400 1120 1000 X