Three portions of the same liquid are mixed in a container that prevents the exchange of heat with the environment. Portion A has a mass m and a temperature of 94.0 oC, portion B also has a mass m but a temperature of 78.0 oC, and portion C has a mass mC and a temperature of 34.0 oC. What must be the mass of portion C so that the final temperature Tf of the three-portion mixture is Tf = 50.0 oC? Express your answer in terms of m; for example, mC = 2.20 m.