Please show each step in solving the following problems:
A.) A carpenter needs to design a frame for a rectangular sandbox. Find the dimensions of the sandbox (height, width, and length) that would provide the maximum surface area of sand, if the total volume of the sand has to be 3 meters^2, and the base of the box is a square (length=width).
B.) A farmer plans to fence a rectangular pasture adjacent to the river. The pasture must contain 12,000 square feet. No fencing is needed along the river. What dimensions will require the least amount if fencing?