It says whose base lies in R. So the base would look like that. It would actually be the X value that corresponds to that particular Y value. So I'll just write X right over here. And then the height is Y. So the height is going to be whatever our Y value is. And then if we wanted to calculate the volume of just a little bit, a slice that has an infinitesimal depth, we could think about that infinitesimal depth in terms of Y. So we could say its depth right over here is DY, DY.