ok
I'll calculate the surface area to answer your question.
Area of the base and top = 2x20x7 = 280 in^2
Area of the frontal and behind faces = 2 x 7x7.5 = 105 in^2
Area of the left and right faces = 2x20x7.5 = 300 in^2
Total area = 280 + 105 + 300
= 685 in^2
The amount of wood needed is 685 in^2
