To help you get a grasp on those nebulous solids of revolution and solids with known cross sections, you will be handcrafting a couple 3-D models
Obviously, these solids of revolution are based upon the disk method, but yours will be composed of washers. More specifically, yours will be half washers, since you only have to construct your model based upon the top-half of the solid.
Scratch work drawings by a couple of calculus students. With a scale of 1 unit to 2 centimeters, the diameter of each washer may, in fact, NOT be 12 cm as shown in the image...