Final answer:
After subtracting the cost of the bookmark, divide the remaining amount by three to find that each book costs $9.
Step-by-step explanation:
The student is asking how much each book costs when buying a bookmark and three books for a total of $28, with the bookmark costing $1.
To solve this problem, you first need to deduct the cost of the bookmark from the total amount spent to find out how much money was spent on books. Since the bookmark cost $1, you subtract $1 from $28, which leaves $27 for the three books.
Now, to find the cost of each book, you divide the total money spent on books by the number of books. So, you divide $27 by 3, which gives you $9 per book.