This chapter asks you to draw two overlapping spheres. The trick in drawing two sphere—one behind the other—is to actually draw two overlapping spheres and simply use the eraser to get rid of the intersecting line (either the left or the right one).
Usually, the sphere that’s behind the closest one to you is smaller. For this exercise, just make sure you draw the sphere in front, slightly below the one behind it.
In the bonus round, I tried to draw two tennis balls. Again, I didn’t any actual Tennis bells, so I copied what was in the book.