b) A truck is hired to transport goods from a factory to a warehouse. The driver's wages are figured by the hour and so are inversely proportional to the speed at which the truck is driven. The cost of gasoline is directly proportional to the speed. Express the total cost of operating the truck as a function of the speed at which it is driven.
c) A bookstore can obtain a certain book from the publisher at a cost of 12 USD per copy. The bookstore has been offering the book at the price of 30 USD per copy, and at this price, has been selling 200 copies a month. The bookstore is planning to lower its price to stimulate sales and estimates that for each 1 USD reduction in the price, 20 more books will be sold each month. Express the bookstore's monthly profit from the sale of this book as a function of the selling price, draw the graph, and estimate the optimal selling price.
d) A tour-bus company in New York has adopted the following pricing policy for groups that wish to charter its buses. Groups containing no more than 40 people will be charged a fixed amount of 2400 USD (40 times 60). In groups containing between 40 and 80 people, everyone will pay 60 minus 50 cents for each person in excess of 40. The company's lowest fare of 40 per person will be offered to groups that have 80 members or more. Express the bus company's revenue as a function of the size of the group. Draw the graph.​