At a supermarket, a 6-ounce bottle of brand A salad dressing costs $1.56. A 14-ounce bottle costs $3.36. A 20-ounce bottle costs $5.60. What unit prices do you need to know to find the best buy? What is the best buy?

1) If 6 ounce bottles of Brand A salad dressing costs = $1.56

Cost of 1 ounce bottle = $1.56:6

Here, cost of one ounce Bottle = $0.26

2) if 14 - ounce bottle costs = $3.36

Cost of 1 ounce bottle = $3.36:14

Here, cost of one ounce Bottle = $0.24

3) if 20 - ounce bottle costs = $5.60

Cost of 1 ounce bottle = $5.60:20

Here, cost of one ounce Bottle = $0.28

Hence, the best price is $0.24 per ounce

Hence, we should buy 14 ounce bottle costs $3.36

You need to know the cost per ounce, or how many cents per one ounce, and the best buy is the 14-ounce bottle.