9. Find two numbers whose sum is 13 and whose product is a maximum. 10. Find two numbers who sum is 19 and whose product is a maximum. 11. Find two numbers whose difference is 13 and whose product is a minimum. 12. Find two numbers whose difference is 19 and whose product is a minimum. 13. Find two positive numbers whose product is 13 and whose sum is a minimum. 14. Find two positive numbers whose product is 19 and whose sum is a minimum. 15. Find the dimensions of a rectangle with an area of 200 square foot that has the minimum perimeter. 16. Find the dimensions of a rectangle with an area of 108 square foot that has the minimum perimeter. 17. Find the dimensions of a rectangle with a perimeter of 148 feet that has the maximum area. 18. Find the dimensions of a rectangle with a perimeter of 76 feet that has the maximum area. 19. Maximum Revenue and Profit A company manufactures and sells r smartphones per week. The weekly price-demand and cost equations are, respectively, p = 500 -0.4r and C(x) = 20, 000 + 20r (A) What price should the company charge for the phones, and how many phones should be produced to maximize the weekly revenue? What is the maximum wockly revenue? (B) What is the maximum weekly profit? How much should the company charge for the phones, and how many phones should be produced to realize the maximum weekly profit