13. The resale value of a certain industrial machine decreases at a rate that changes with time. When the machine is t years old, the rate at which its value is changing is 200: 1200 dollars per year. When the machine was one year old it was worth $8900. How much will it be worth when it is 5 years old? 13. [10 pts.] [4. Use calculus to nd the following for the function f(x) =2:3 9i:2 24x+15 . [15 pts.] a. The relative maximum point a. b. The relative minimum point c. The inection point