That is the formula for the volume of a rectangular solid. A box is not solid! 20x 12 x 9 cubic centimeter is the volume of the box including the interior. Since each side is 1 cm thick, the interior is 18 by 10 by 7 cm.
That is the formula for the volume of a rectangular solid. A box is not solid! 20x 12 x 9 cubic centimeter is the volume of the box including the interior. Since each side is 1 cm thick, the interior is 18 by 10 by 7 cm.
What you want is the volume of the WOOD. To evaluate this, you need to evaluate the volume of the entire amount of space up to the boundaries (i.e. 20 x 12 x 9 = 2160) and subtract the "empty space" (i.e. 18 x 10 x 7 = 1260).