Assuming ideal gas behavior, we can add the moles of two different substances when they have the same pressure, temperature and volume conditions. Using the ideal gas equation:
PV = nRT
V = nRT/P
V = (0.522+0.522 mol)(0.0821 L-atm/mol-K)(42.7+273 K)/(0.56 atm)
V = 48.32 L
