If you just paint the surface of the cube, then the inside of the cube would not have any of their faces painted red.
Just looking at the cube from a side view, you would realize that there would be a smaller cube, 6 x 6 x 6 (not 7 since you have to account for both the top side and the bottom side), and so that is the answer, 6 ^ 3, which is 216.
