You must be able to write a stoichiometrically balanced equation:
Either equation is acceptable. The arithmetic may be simpler if we use the second.
The starting conditions specify a
Note that quantitative reaction would be an absolutely absurd outcome for this reaction. In the industrial process the reactants are cycled to achieve reasonable conversions. The one thing the reaction has got going for it is that the ammonia product is condensable, whereas the reactant gases are relatively incondensable. I should add that this reaction, this fixation, is probably the most important inorganic reaction that humans perform. See here for further details.