The answer is A because if you divide 59.50/7 you would get 8.50, and 8.50 x 8 is 68! You can easily eliminate any other answer choices if the distance between the values is not equal!
If you divide $59.50 by 7 you get 8.5. Which would be $8.50. You can then go through each table and multiply the cost of one book with how many books are being bought. So yeah. Hope this helps
