The molar masses of CaCO3,N2 and NH2CONH2 are 100 g/mol, 28 g/mol and 60 g/mol respectively.
1 mole of CaCO3 and 1 mole of N2 gives 1 mole of urea as per the stoichiometry.
Thus, 100 kg of CaCO3 and 28 kg of N2 gives 60 kg of urea.
However, the yields are less than 100%.
Hence, mass of nitrogen required Y=280.9=31 kg.
Mass of CaCO3 required X=1000.50=200 kg.
Hence, X+Y=200 kg +31 kg =231 kg.