The trick to answering this question is to realize that the question is about average sales.
So once you have the average monthly sales for the entire several year period, you can calculate the average sales for any number of years within the period as well.
For example, if the average monthly sales were 100. Then the average sales for 12 months, in other words one year, would be 1200.
Statement 1:
This gives us no quantity for sales that could be used to calculate average sales.
Insufficient.
Statement 2:
This provides the average monthly sales, which can then be used to calculate the average biannual, in other words two year, in other words twenty-four month, sales.
Sufficient.
The correct answer is B.
Cute question.
