Teacher's Note: This description gives the variable formulation and may be omitted in favor of a diagram to be labeled.

The basic approach will be to make a cross shaped flat piece consisting of a y" (vertical) by z" (horizontal) rectangle at the center with x"(horizontal) by y" (vertical) rectangles on both sides and x" by z" rectangles on top and bottom of the center rectangle. Finally a y" by z" rectangle will be centrally located at the bottom of the bottom x" by y" rectangle and will serve as a cover for the enclosed box.