To find the combined volume, you will need to find the volume of the square pyramid and the rectangular prism.
V = 1/3 Bh (volume of pyramid); B is the area of the base.
1/3 x 8 x 8 x 3
V = 64 cubic inches
V = Bh (volume of prism)
8 x 8 x 4
V = 256 cubic inches
256 cubic inches + 64 cubic inches = 320 cubic inches.
The entire volume is 320 cubic inches.