To find the volume of a rectangular pyramid, we use the formula V = (1/3) * base area * height.
First, we need to find the base area. The base of the pyramid is a rectangle with a length of 14 inches and a width of 6 inches. Therefore, the base area is 14 * 6 = 84 square inches.
Next, we plug in the base area and the perpendicular height of 12 inches into the formula:
V = (1/3) * 84 * 12 = 336 cubic inches
Therefore, the rectangular pyramid contains 336 cubic inches. The closest answer choice is 336 in.3.