The edge length of the large cube is twice that of the small cube, and the volume of the large cube is 21 cubic decimeters more than that of the small cube. What is the volume of the small cube?

The edge length of the large cube is twice that of the small cube, and the volume of the large cube is 21 cubic decimeters more than that of the small cube. What is the volume of the small cube?

21 (8-1) = 3 (cubic decimeter), a: the volume of small cube is 3 cubic decimeter