Hey there!
Na + H₂O → NaOH + H₂
First, balance O.
One on the left, one on the right. Already balanced.
Next, balance H.
Two on the left, three on the right. Let's add a coefficient of 2 in front of NaOH and a coefficient of 2 in front of H₂O, so we have 4 on each side.
Na + 2H₂O → 2NaOH + H₂
Lastly, balance Na.
One on the left, two on the right. Add a coefficient of 2 in front of Na.
2Na + 2H₂O → 2NaOH + H₂
This is our final balanced equation.
Hope this helps!