A publisher estimates that the cost of producing between 1,000 and 10,000 copies of a certain textbook is $50 per copy; between 10,001 and 20,000, the cost is $40 per copy; and between 20,001 and 50,000, the cost is $35 per copy.

a. Find a function F(N) that gives the total cost of producing N copies of the text for 1,000 ≤ N ≤ 50,000.

b. Sketch the graph of the function F(N) you found in part (a).