Richard is asked to spray wash the exterior of a building that is shaped like a cube. He decides to calculate the surface area of the building in order to estimate how much water he will need. He does the calculation using the standard formula and, after doing the job, realizes he overestimated the amount of water he needed. Where was his mistake?
A) He forgot that there is no formula for the surface area of a cube.
B) He forgot to add the area of the base to the total surface are of the cube.
C) He forgot to square the result.
D) He forgot to subtract the area of the base from the total surface area of the cube.