The formula of the volume of a sphere is (4*pi/3)*R^3. You said you know how calculate the ratios. Can you continue from there?
Planet Aniram is similar to Planet Semirg, both of which are perfect sphere. If the ratio of the length of Planet Aniramís radius to the length of Planet Semirgís radius is 3:4, then find the volume of Planet Semirg in cubic units if the volume of Planet Aniram is 135 cubic units.
I know how to find the ration, you divide by 3 but I don't know how to find the volume in cubic units.
The condition that they are both perfect spheres is redundant, that they are similar is sufficient.