So let's see if we can set up the integral. And maybe then in the next video, we'll just forge ahead and actually evaluate the integral. So let's think about the volume of the washer. To think about the volume of the washer, we really just have to think about the area of the face of the washer. So area of face is going to be equal to what? Well, it would be the area of the washer, if it wasn't a washer, if it was just a coin, and then subtract out the area of the part that you're cutting out. So the area of the washer, if it didn't have a hole in the middle, would just be pi times the outer radius squared.