Social Benefit = Private Benefit + External Benefit (Positive Externalities)
Social benefits is a combination of the private benefits and the external benefits. In other words, it is the total benefit to society caused from the production of a good/service. Private benefit is the benefits for the firms producing the good/service and external benefits are the benefits to society. An example of private benefits from education are the money from the parents and the external benefit would be having a more educated society. Social benefit would be a combination of these two so the social benefits would include both the money from parents and a more educated society.