The economic concepts that will be used in this case are explained below:
Need/Want: A need is a good or service that's needed by an economic agent such as an individual to survive. Examples of needs are clothes, shelter, food etc.
On the other hand, wants represents the goods that we desire as individuals but can live without them. Examples of wants are phones, cars, bicycles etc.
Regarding the question, Frankie should analyze properly if the pair of shoes are either a need or a want. If he considers the shoes to be a need, then he should buy them as they are important. If they're want, then it's not compulsory that he buys the shoes.
Opportunity cost: Also, he should consider the opportunity cost of buying the shoes. In this case, he should properly analyze the trade off and know of he could spend the money that he'll use in buying the shoes on something that's more beneficial to him than the shoes.
