"peter and mary have been married for several years". peter has been unhappy for several months and is thinking about initiating a divorce. he decides to make a list of the benefits and costs of the relationship. peter is using a form of which theory?

I would say the correct answer is the exchange theory.
This theory proposes the idea that human relationships consist of pros and cons, and that each person is always evaluating his or her relationships based on those benefits and costs. If the benefits outweigh the costs, the most likely scenario is that that person will stay in a relationship - if it's the opposite, the relationship is likely to end.

3. i would say one, but one is not prime nor composite.