Well, let's just think about it disk by disk. So let's construct a disk right over here. And we've done this many, many, many times already, where we essentially want the volume of each of these disks, and then we're going to take this for each of these x's in our interval, and then we're going to take the sum of the volumes of all of the disks and we're going to find the volume. We're going to stack them all up, or I guess put them next to each other in this case, and find the volume of our entire figure. So to figure out the volume of each disk, we just have to figure out the area of its face, and I'll do that in purple. We just have to figure out the area of the face and multiply it by the depth. So what's the area of this face?