There are several important information's already given in the question. Based on those given information's the answer can be easily deduced.
Ratio of the radii of two spheres = 9 : 2
then
Ratio of the volume of the two spheres = 9^3 : 2^3
= 729 : 8
I hope that this is the answer that you were looking for and the answer has actually come to your desired help.
