We know the number of cubes needed to fill the prism, and we know the edge length of cubes, so to find the volume of the prism, we can find the volume of *each cube* and then multiply that by the number of cubes.
Volume of the small cubes:
13 x 13 x 13 = 2,197 cubic in.
Volume of the prism:
2,197 x 3996 = 8,779,212 cubic in.