Hey there!
Assuming you want the equation balanced:
NH₄NO₃ → N₂O + H₂O
Balance N.
2 on the left, 2 on the right. Already balanced.
Balance H.
4 on the left, 2 on the right. Add a coefficient of 2 in front of H₂O.
NH₄NO₃ → N₂O + 2H₂O
Balance O.
3 on the left, 3 on the right. Already balanced.
Your final balanced equation:
NH₄NO₃ → N₂O + 2H₂O
Hope this helps!