Two rigid boxes 1/2 containing different ideal gases are placed on a table. Box A contains one mole of nitrogen at temperature T0 , while Box B contains one mole of helium at temperature (7/3) T0. The boxes are then put into thermal contact with each other and heat flows between them until the gases reach a common final temperature. (Ignore the heat capacity of boxes). Then, the final temperature of the gases, Tf , in terms of T0 is