Answer:
a. John works the night shift,and night hours are less desirable for most workers.
Step-by-step explanation:
The Equal Pay Act of 1963 established that employees must earn the same wage for similar jobs performed regardless of their gender. This means that you cannot pay someone more for being a men if the job done is the same. If any difference in wages exist, it must be justifiable in some way, e.g. different responsibilities, different labor conditions, serve different markets, etc.
In this case, since fewer people want to work on the night shift, in order to attract workers, the company might pay more for doing so. US laws does not require for night shifts to be paid higher wages, but the law of demand and supply might be responsible for the higher wages (demand and supply of labor).