Answer: The best deal available is option D; 12 pack for $15.00
Step-by-step explanation: Each pack comes with its own price per quantity and the quantity also varies with each deal/pack. In order to find which pack offers the best deal, we shall examine the cost per pen for each deal and the pack which turns out to have the cheapest price for a single pen in each pack shall be the best deal.
Option A; 4 pack for $7.00
This means each pen in this pack shall cost
Per pen = 7.00/4
Per pen = 1.75
Option B; 6 pack for $10.25
Each pen in this pack shall cost
Per pen = 10.25/6
Per pen = 1.708
Per pen ≈ 1.71
Option C; 10 pack for $13.00
Each pen in this pack shall cost
Per pen = 13.00/10
Per pen = 1.30
Option D; 12 pack for $15.00
Each pen in this pack shall cost;
Per pen = 15.00/12
Per pen = 1.25
Option E; 25 pack for $32.50
Each pen in this pack shall cost;
Per pen = 32.50/25
Per Pen = 1.30
From the calculations shown, the best deal is option D, because at that rate, you would be paying $1.25 per pen, that is when you buy 12 pack for $15.00