So it's going to be 4 minus x squared plus 2x squared. Minus pi times the inner radius, although we factored out the pi. So minus the inner radius squared. So minus 4 minus x squared. So this will give us the surface, the surface there, or the area of the surface or the face of one of these washers. If we want the volume of one of those washers, we then just have to multiply times the depth dx. We just multiply times the depth dx.