EDIT:

NVM, I verified it.

/EDIT

Suppose you make napkin rings by drilling holes with different diameters through two wooden balls( which also have different diameters). You discover that both napkin rings have the same height h, as shown in the figure.

(a) Guess which ring has more wood in it.

(b) Check your guess: Use cylindrical shells to compute the volume of a napkin ring created by drilling a hole with radius r through the center of a sphere of radius R and express the answer in terms of h.

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For b, I got that they have the same volume. That was my interpretation after finally getting:

Can anyone tell me if this is correct? If it is, then I don't need any more help, if not, I'll have to post my work.