The cost of a food item at 2 different stores is shown. What is the unit price at each store and tell where the item costs less?

Store A: $3.20 for 16oz of walnuts. Store C: $2.13 for 3lbs of potatoes.
Store B: $2.30 for 10oz of walnuts. Store D: $3.35 for 5lbs of potatoes.