The surface area of the box is being referred to as A The surface area will be the sum of the four rectangular sides' areas and the base area. Base area = x² Rectangular side area = xh A = x² + 4xh Volume is, as you said, V = x²h Lets substitute h from the formula of A to obtain A in our final answer. Substituting x is possible, but more difficult (A - x²)/4x = h V = (x²) * (A - x²)/4x V = (Ax - x³)/4