3 A rectangular box with a volume of 125 cubic inches has a square base Find a function that models its surface area S in terms of the length z of one side of its base 4 A farmer has 2400ft of fencing and wants to fence off a rectangular field that borders a straight river He does not need a fence along the river s edge What are the dimensions of the field of the largest land area that he can fence off Hint Model the problem in one of two ways either using the length and or using the width Then find the maximum value of the function Use that to determine the field s dimensions length and width