I think we can all agree that 1 centimeter=10millimeters.
And if x is the side in centimeters then 10x will be the side in millimeters.
We just need to rewrite x^3 into (10x)^3.
Because you need to do the exponent to all part of the ( )...
(10x)^3=1000x^3
V(x)=1000x^3 cubic millimeters is the answer