And then just to make the face of the washer a little bit clearer, let me do it in this green color. So the face of the washer is going to be all of this business. So if we can figure out the volume of one of these washers for a given x, then we just have to sum up all of the washers for all of the x's in our interval. 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.