The number of cubic feet in the volume of a cube is the same as the number of square inches in its surface area. The length of the edge in feet is:

- 6
- 864
- 1728
- 6 · 1728
- 2304

Let *s* represent the length of an edge in feet. Then:

Volume = *s*^{3} cubic feet.

The surface area is 6*s*^{2} square feet. There are 144 square inches in 1 square foot.

So the surface area is 6 · *s*^{2} · 144 = 864*s*^{2} square inches.

So *s*^{3} = 864*s*^{2} → s = 864 feet. The answer is (b).

Check:

V = 864^{3} = 644,972,544 cubic feet. An edge is 864 · 12 = 10,368 inches.

Surface area = 6 · 10368^{2} = 644,972,544 square inches. Ok.