An insulated tank initially contains 0.25 kg of a gas with an internal energy of 200 kJ/kg. Additional gas with an internal energy of 300 d/kg and an enthalpy of 400 Id/kg enters the tank until the total mass of gas contained is 1 kg. What is the final internal energy (in Id/kg) of the gas in the tank?
a. 250 b. 275
c. 350 d. None of above