Answer:
The total surface area of a rectangular prism or cube is equal to the sum of the areas of each side.
The area of each side is equal to its length multiplied by its width or A = L x W.
Since the areas of opposite sides are equal, multiple each side area by 2 to obtain the areas of opposite sides.
where:
L = length
W = width
H = height
total area = (2)(L)(W) + (2)(L)(H) + (2)(W)(H)
or simplified:
total area = 2[(L)(W) + (L)(H) + (W)(H)]