So area is equal to pi r squared, which means that the area of this thing is going to be pi times our radius squared. Our radius is square root of y. So this thing is going to be equal to pi squared of y squared is just pi times y. Now, if we want the volume, we just have to multiply the area of the surface times the depth, times dy. So the volume of each of those disks is going to be pi y times dy. This gives you the volume of a disk. Now, if we want the volume of this entire thing, we just have to sum all of these disks for all the y values between y is equal to 1 and y is equal to 4.