Professors Adams and Brown make up the entire demand side of the market for summer research assistants

Question:

Professors Adams and Brown make up the entire demand side of the market for summer research assistants in the economics department. If Adams’s demand curve is P = 50 - 2QA and Brown’s is P = 50 - Q B , where QA and QB are the hours demanded by Adams and Brown, respectively, what is the market demand for research hours in the economics department?