The key to this problem is to determine for which of the two products can you purchase the most of the same amount. To do that, you simply determine the volume of product/ dollar amount.
For the first product, (15 oz/2.25) = 6.7 oz/ dollar
For the second product, (20 oz/ 3.40) = 5.9 oz/ dollar
Thus, choice A is the better value as you can purchase more product for the same amount.