Calculate the mole fraction of each component and the gas constant of the mixture for each of

Question:

Calculate the mole fraction of each component and the gas constant of the mixture for each of the following mixtures:
a) 4 kg N2, 1 kg O2, 3 kg CO2
b) 4 kg N2, 1 kg CH2, 3 kg NH3
c) 5 kg air, 3 kg CO2
d) 3 kmol CH4, 4 kmol N2, 3 kmol NH3
e) 5 kmol air, 3 kmol CO2