In order to solve this exercise you need to analyze the information given:
1. The amount of trail mix Aracely has is:

2. Those pounds are divided in 8 equal parts to put them in 8 bags.
Remember that a fraction has the following form:

Where "a" is the numerator and "b" is the denominator. Both are Integers.
A fraction also indicates a division. Therefore, since you need to divide 3 pounds by 8, you can set up the following:

The answer is: Option B