Here, think of it this way. The prism has 1120 cubes. What's the formula for the volume of a cube?
It's v=a^3, a being the length of a side. Since we know the length...
V=12^3, which equals 1728. So each cube has a volume of 1728 inches. Now, multiply that by 1120. You get...
1,935,360!
Hope this helps!