It's essentially the ring generated if you were to take this rectangle, this rectangle of height dy and rotate it around the line x equals 2. And we're going to construct a ring like that for each of the y's in our interval. So you can imagine stacking up a whole set of rings just like this and then taking the sum of the volumes of all of those rings and the limit of that sum as you have an infinite number of rings with, or close to infinite, or really infinite number of rings with infinitesimally small height or depth or dy. So let's figure out how we would do this. Well, we know that all we have to do is figure out what the volume of one of these rings are for a given y as a function of y and then integrate along all of them, sum them all up. So let's figure out what the volume of one of these rings are. And to do it, we're going to express these functions as functions of y.