Answer:
Each book cost about $6.20 per book, or in more general terms, $6 per book.
Explanation:
If you round the $30.85 total of 5 books to $31 and divide that by 5, you get an average cost of $6.20 per book.
If you need a more general answer, you could round the $30.85 total of 5 books to $30 and divide that by 5, you get an average cost of $6 per book.