13. Sketch a picture of a function with the given characteristics. f(x) < 0 when x > 0 f(x) > 0 when x < 0 f(x) = 0 when x = 0 f(x) is decreasing on the interval (-, -3) and (-1,0) f(x) is increasing on the interval (-3,-1) f(x) is concave up on the interval (-, -3) and (0,4) f(x) is concave down on the interval (-3,0) and (4,)