Final answer:
To determine which package of chocolate to purchase based on unit pricing theory, compare the cost per ounce of each package. Package A has a lower cost per ounce compared to package B, so you should purchase package A.
Step-by-step explanation:
To determine which package of chocolate to purchase based on unit pricing theory, we need to compare the cost per ounce of each package. Package A costs $14 for 18 ounces, so the cost per ounce is $14/18 = $0.78. Package B costs $18 for 21 ounces, so the cost per ounce is $18/21 = $0.86. Based on unit pricing theory, we should purchase package A because it has a lower cost per ounce compared to package B.