a$.$ An educational software company wants to expand the number of economics questions that it offers and is considering hiring another economist. The company compares how much adding another worker will improve the product to the additional cost.

b$.$ Ava finds that there is not enough time after work to have dinner, exercise, and watch TV$,$ and she must make choices about how to use her limited time.

c$.$ On Black Friday, there are huge sales for electronics at many retailers. David must decide between buying a new iPhone or a new Apple watch.