Construction Cost. A fence is to be built to enclose a rectangular area of 800 square feet. The fence along three sides is to be made of the material...

Construction Cost. A fence is to be built to enclose a rectangular area of 800 square feet. The fence along three sides is to be made of the material that costs 6 dollars per foot. The material for the fourth side costs 18 dollars per foot. Find the dimensions of the requitable that will minimize the total cost of the fence.