Hey there :)
The volume formula of a cylinder is:
V =

r²h
The volume of the larger volume is given to be 9648³ and the height is 18 in
We need to find the radius first
9648 =

r²(18)

=

r²
536 =

r²

= r²

= r
r ≈ 13.06
The ratio of the big cylinder to small cylinder is:
18 : 9 (given height)
So the big cylinder is
2 times bigger than the small cylinder
Therefore the radius of the big cylinder is as well 2 times bigger

r ≈ 6.53 ( the radius of the small radius )
V (of small cylinder) =

(6.53)²(9)
= 1206 in³