here for the general method.
1. A parcel delivery service will deliver a package only if the length plus the girth (distance around) does not exceed 100 inches. Find the maximum volume of a recatngular box with quare ends that satisfies the delivery company's requirement.
2. A fence is to be built enclose a rectangular area of 270 square feet. The fence along three sides is to be made of material that costs 6 dollars per foot, and the material for the fourth side costs 12 dollars per foot. Find the lengh and width of the enclosure that is most economical to construct.