In this case we must divide the area into two parts, in the prism and in the pyramid, the sum of the volume of these parts would be the total volume
However
for the volume of the prism it would be the multiplication of the three sides, that is:
8 * 8 * 9 = 576
i.e. 576 ft ^ 3
For the pyramid, the formula is the multiplication of the area of the base by the height divided by 3, we know that the area of the base is 8 * 8 and that the height is 3, therefore:
