Originally Posted by
Soroban Hello, BabyMilo!
Let $\displaystyle r$ = radius of the small tank.
Let $\displaystyle h$ = height of the small tank.
The volume of the small tank is: .$\displaystyle v \:=\:\pi r^2h\;=\;40$ litres.
The radius of the large tank is: . $\displaystyle R = 3r$
The height of the large tank is: .$\displaystyle H = 2h$
The volume of the large tank is: .$\displaystyle V \:=\:\pi R^2H \:=\:\pi (3r)^2(2h)$
So we have: .$\displaystyle V \;=\;18\underbrace{\pi r^2h }$
. . . . . . . . . $\displaystyle ^{\text{This is the volume of the small tank}}$
Therefore: .$\displaystyle V \:=\:18(40) \:=\:720$ litres.