To find how much space remains in the box, you will find the total space of the box by finding the volume of it. Then you will subtract the volumes of the 2 triangular prisms. The remaining would be the extra space.
Volume of Rectangular Prism - 2(Volume of the Triangular Prism) Bh - Bh (3 x 6 x 4) - 2 [(1/2 x 2 x 5) x 3] 72 cubic feet - 30 cubic feet 42 cubic feet
