So the area of the face for a particular x is going to be equal to pi times f of x squared. In this case, f of x is x squared. Now what's our volume going to be? Well, our volume is going to be our area times the depth here. It's going to be that times the depth times dx. So the volume of this thing right over here, so the volume just of this coin, I guess you could call it, is going to be equal to my area times dx, which is equal to pi times x squared squared. So it's equal to pi x squared squared is x to the fourth.