C₂H₆ + O₂ ----> CO₂ + H₂O
In order for an equation to be balanced there must be the same number of each atom on both sides
On the left side currently we have 2 C, 6 H, and 2 O
On the right side currently we have 1 C, 2 H, and 3 O
2C₂H₆ + 7O₂ ----> 4CO₂ + 6H₂O
Start by putting a 2 in front of C₂H₆
2C₂H₆ + O₂ ----> CO₂ + H₂O
we now have 4 Carbons on the left, so we need 4 carbons on the CO₂
2C₂H₆ + O₂ ----> 4CO₂ + H₂O
We also now have 12 H on the Left so we need to add a 6 to H₂O
2C₂H₆ + O₂ ----> 4CO₂ + 6H₂O
Finally with Oxygen we have 14 on the right side so we need to add a 7 to O₂
2C₂H₆ + 7O₂ ----> 4CO₂ + 6H₂O
Hope this helped!