Answer:
<h2>P = 6.25n</h2>
Step-by-step explanation:
The problem says that each set costs $6.25, and <em>n </em>refers to sets of pencils.
So, we know that "per" refers to multiplication, because if each set of pencil costs $6.25, then a <em>n </em>quantity of pencils will be the sum of $6.25 <em>n </em>times, which is the definition of multiplication. So, the equation that correctly determined the price is:

The price is $6.25 per set of pencils, that is what this equation says.
Therefore, the right answer is the second one.