Hey there!
C₂H₄ + O₂ → CO₂ + H₂O
First let's balance C.
There are 2 on the left and 1 on the right. So, let's add a coefficient of 2 in front of CO₂.
C₂H₄ + O₂ → 2CO₂ + H₂O
Next let's balance H.
There are 4 on the left and 2 on the right. So, let's add a coefficient of 2 in front of H₂O.
C₂H₄ + O₂ → 2CO₂ + 2H₂O
Lastly, let's balance O.
There are 2 on the left and 6 on the right. So, let's add a coefficient of 3 in front of O₂.
C₂H₄ + 3O₂ → 2CO₂ + 2H₂O
Here is our final balanced equation.
Hope this helps!