The length of the side of the cube has m cm, so the volume must be ...
[tex] {m}^{3} [/tex]
And the other cube has a length of n cm, so the volume must be ...
[tex] {n}^{3} [/tex]
Then the volume of the space between is equal to the difference of their volumes, therefore ...
[tex] {n}^{3} - {m}^{3} [/tex]
