The answer is 3
This is because to find the volume of X, you just do the side length of X^3, and to find the volume of Y, you do Y^3.
Since both of these values are to the power 3 (X^3 and Y^3), you need to undo it to find the side length of X divided by the side length of Y, and to undo this you need to do something called cube rooting
And the cuberoot of 27=3