Which theory states that social interaction between people is based on the efforts of each person to maximize rewards and minimize costs?

I believe the answer is the social exchange theory

the social exchange theory is based on the assumption that all people are individualistic in nature.

This theory believes that human only choose to interact with another human only if the benefit from interacting with that other human surpass the cost to interact with him. (which explains the reason some people choose to marry old - rich individuals despite negative perception that will be labeled to them)