This is a psychometric problem. For these, use the molecular weights (found on any periodic table) and the molar ratios in the equation to solve for a limiting reagent, then from that calculation you derive the theoretical yield:
Molecular weights:
H2 = 1.01 g/mol * 2 H atoms = 2.02 g/mol
N2 = 14.01 g/mol * 2 N atoms = 28.02 g/mol
NH3 = 14.01 g/mol * 1 N atom + 1.01 g/mol * 3 H atoms = 17.04 g/mol
mol = Molecular
