The graph below shows a company's profit f(x), in dollars, depending on the price of pens x, in dollars, being sold by the company: 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? part b: what is an approximate average rate of change of the graph from x = 3 to x = 5, and what does this rate represent?