A) A car rental agency has 24 cars (each an identical model). The owner of the agency finds that at a price of $18/day, all the cars can be rented; however, for each $1 increase in the cost, one of the cars is not rented. What should the agency charge to maximize income?

B) A fence is to be built to enclose a rectangular area of 220 square feet. The fence along three sides is to be made of material that costs $5 per foot, and the fourth side costs $13 per foot. Find the length L and width W (with W < L) of the enclosure that is most economical to construct.

C) Find the dimensions of the rectangle of greatest possible area that can be inscribed in a semicircle of radius 6.