Jim and Frank Mysteries Solutions - Puzzle #46 - Bookworm

Oooh, sneaky, you'll have to notice that the books are ordered back to front so the little worm actually only eats one cover of volume one, all of books 2,3 & 4, and again only the one cover of volume 5, making a sum total of 19cm (0.5 + 6 + 6 + 6 + 0.5).