Average floor space of each bookshelf: 144÷ 12= 12 (square meter).

A: On average, each bookshelf covers an area of 12 square meters.

Solution: Given that "the librarian is 18m and the width is 8m", it can be calculated that the library covers an area of18× 8 =144 (m2); So according to the known "there are 12 bookshelves in the museum", how many square meters does each bookshelf occupy on average? , it is necessary to use "total library area ÷ number of shelves = average area of each shelf" to calculate: 144÷ 12= 12 (square meter).

So, the process of solving the problem is:

Library area: 18×8= 144 (m2)

Average floor space of each bookshelf: 144÷ 12= 12 (square meter).

A: On average, each bookshelf covers an area of 12 square meters.