A rectangular box with a square base and no lid must have a total surface area of 20 cm2 (so the combined area of the five sides of the box is 20 cm2 ). Find the dimensions of the box (length, width and height) so that the total volume is as large as possible.

The length of a rectangular board is 3 feet less than twice its width. a second rectangular board is such that each of its dimensions is the reciprocal of the corresponding dimensions of the first rectangular board. if the perimeter of the second board is one-fifth the perimeter of the first, what is the perimeter of the first rectangular board?