Suppose you have 78 feet of fencing to enclose a rectangular dog pen. The function A=39x-X^2, where X=width gives you the area of the dog pen in

Suppose you have 78 feet of fencing to enclose a rectangular dog pen. The function A=39x-X^2, where X=width gives you the area of the dog pen in square feet . What width gives you the maximum area ? What is the maximum area? Round to the nearest tenth