This question is trying to assess your understanding of the concept of Stoichiometry.
In order to solve this question, first you need to have a balanced reaction.
That is: N2+3H2 —> 2NH3
Now that we have a balanced reaction, we can start our conversions:
Note that since the question is stating that we have sufficient Nitrogen present, we do not need to worry about Nitrogen running out during our reaction (being the limiting reactant).
So, we can simply see how much NH3 is produced from 4moles of H2 by following steps below:
Using the balanced reaction, we can use the ratios to figure out how many moles of NH3 will be produced.
4mol H2 x (2NH3/3H2) = 2.667mol NH3
Now that we have the NH3 in moles, we can convert that to grams of NH3 using the molar mass:
2.667 mol NH3 x (17grams/1mol NH3)= 45.34g NH3
I hope this helps :)