Cavalieri's Rule tells us that it doesn't matter if the shape is oblique or not, the volume is still found using the regular volume formula. For a pyramid, this formula is V = 1/3 Bh, with B being the area of the base which is a rectangle. The area is 10*12 which is 120, and the height is given as 8. So the volume is V = 1/3 * 120 * 8, which is 320 units cubed.
