If the ratio of the radii of two spheres is 8: 9, what is the ratio of the volumes of the two speheres

Let 
A> smaller sphere
B> larger sphere
radius of sphere A> rA
radius of sphere B> rB

we know that
rA/rB=8/9
the scale factor is equal to 8/9
volume smaller sphere A=[scale factor]³*volume larger sphere B
volume smaller sphere A/volume larger sphere B=[scale factor]³
volume smaller sphere A/volume larger sphere B=[8/9]³> 512/729

the answer is
512/729

I’m confused what’s happening