So the outer circle radius, so it's going to be pi times outer radius squared minus pi times inner radius squared. And we want this all to be a function of y. So the outer radius as a function of y is going to be what? Well, it might be easier to visualize. Actually, I'll try it both places. So it's this entire distance right over here. Essentially, the distance between the vertical line, the horizontal distance between our vertical line and our outer function, the horizontal distance between our vertical line and our outer function.