A Rigid Insulated Box Contains 20

A rigid insulated box contains 20.0 g of He(g) at 25.0° C and 1.00 atm in one compartment and 20.0 g of N₂(g) at 115° C and 2.00 atm in the other compartment. These compartments are connected by a partition that transmits heat. What is the final temperature in the box at thermal equilibrium? (C_v(He) = 12.5 J/K•mol; C_v(N₂) = 20.7 J/K•mol)

A) 81.0°C
B) 70.0°C
C) 58.9°C
D) 42.3°C
E) none of these