There are story books in the library. A science book is three times less than a story book. 2 1 4a-2 1 means the sum of story books and science books.

Reason: There are 2 1 fewer sci-tech books than story books, so the number of sci-tech books is 3A-2 1.

The total number of sci-tech books and stories is a+(3a-2 1) = 4a-2 1.