Please help me in exercise 4 and exercise 5. I need answer written in PDF.

Exercise 4. {6 points). A cable is to be run from a power plant on one side of a river 900 meters wide to a factory on the other side, 3,000 meters downstream. The cost of running the cable under the water is $5 per meter, while the cost over land is $4 per meter. What is the most economical route over which to run the cable? 900 Exercise 5. (6 points). A bicycle manufacturer buys 6,000 tires a year from a distributor. The ordering fee is $20 per shipment, the storage cost is 96 cents per tire per year, and each tire costs $21. Suppose that the tires are used at a constant rate throughout the year and that each shipment arrives just as the preceding shipment is being used up. How many tires should the manufacturer order each time to minimize cost