Step 1: Find the slope
Every 3 magnets that you buy, you need to pay 1 more dollar. Therefore, if you have 9 magnets, the cost will be 3 dollars. Also, if you have 6 magnets, the cost will be 2 dollars. Finally, if you have 3 magnets, the cost will be 1 dollar. So... the correct options are Options B, E, F
Answer options: B,E,F