Exercise 3 solution

1768 to 1853: 1853 - 1768 = 85 years.
1669 to 1768: 1768 - 1669 = 99 years.

Why the bee space mattered: movable bars alone still let bees glue comb to the walls and to each other. Frames hung at the bee space (commonly 6 to 9 mm) leave a passage the bees do not fill with wax, so each frame slides out without harm and can be returned. That is what made inspection and large-scale commercial honey production practical (as the chapter's article says).