There's a brainteaser that states:

Each of the containers shown above has a radius r of 3 inches and a height of h of 6 inches. IF the cone shaped container is filled with water and this water is then poured into the empty cylindrical container, what will be the depth in inches of the water in the clyindrical container?

So i found out the volume of the both, which turns out to be 18 and 54. So i took the ratio and multiplied that ratio to 18, which in turn gives me 6. But the actual asnwer was 2. Can i have a explanation of how to get there? I guessed the 2 comes from dividing 18 with 9 r^2.