Answer:
2120 books
Explanation:
Let the number of books be

- For the first method, we can write the cost equation as:
Cost =

- For the second method, we can write the cost equation as:
Cost =

Since we want cost to be same, we equate the 2 equations of cost and solve for x, the number of books, to get our answer:

The cost for both methods will be same for 2120 books