If they are similar, and the second cube's length is 3 times that of the first, then all of the sides are 3 times as large.
To calculate the volume, we multiply the length by the width by the height, each of which is 3 times as big. So, in total, the volume is 27 times larger in the second prism than the first.
So, if the first volume is 30 cubic centimetres, the second one would be 810 cubic centimetres.
Hope I helped! xx