The graph below shows a company's profit f(x), in dollars, depending on the price of pencils x, in dollars, being sold by the company:

graph of quadratic function f of x having x intercepts at ordered pairs negative 0, 0 and 10, 0. the vertex is at 5, 160

part a: what do the x-intercepts and maximum value of the graph represent? what are the intervals where the function is increasing and decreasing, and what do they represent about the sale and profit? (6 points)

part b: what is an approximate average rate of change of the graph from x = 2 to x = 5, and what does this rate represent?