Bill and cathy just got married and moved into an old house needing lots of repair. bill is not good at household repair, but he is an excellent chef. cathy cannot cook beyond cereal, but she is excellent at doing household repairs. this is an example of

This is an example of exchange theory.
In sociology, exchange theory has to do with maximizing benefits while also minimizing costs. When applied to Bill and Cathy's situation, they are taking advantage of each other's skills in order to minimize costs - Bill can cook and Cathy can't (so they can prepare food on their own) and Cathy can repair stuff and Bill can't (so they don't have to get a handyman).