To solve this question you would normally have to balance the reaction, but the reaction is already balanced so you can skip that step.
N₂ (g) + 3 H₂ (g) → 2 NH₃ (g)
Next thing you need to do is write down what you are given which is 5.48 moles of Nitrogen. You can use the balanced chemical reaction to convert from moles of one substance to moles of another substance.
(5.48 moles N₂) *( 1 N₂ / 2 NH₃ ) = 2.74 moles NH₃.
When you do this last step you want to make sure you are in moles and not grams.