Final answer:
To find out the cost of buying 9 books at the given rate, the cost per book is needed but not provided in the given information.
Step-by-step explanation:
To find out how much it would cost to buy 9 books at the given rate, we need to multiply the cost per book by the number of books. In this case, the cost per book is not provided in the information given, so we cannot calculate the exact cost.