Well, it is one minus f of x. So that is equal to the radius. So the area, the area of kind of the face of this coin is going to be pi, the area of the face of this coin is going to be pi times the radius squared, which is equal to pi times one minus f of x, one minus f of x squared. That's this blue area right over here. And then if I want to find the volume of this coin, I would multiply it by the depth of the coin. So times dx. And if I wanted to find the volume of this entire solid, this entire rotated solid, I would want to find the sum of all of these volumes.