When balancing a reaction, you first want to count how many particles there are of each element on each side.You then want to try and make both sides the same for each element. In this case we're going to start by balancing the carbon first. To do this, we want to times the carbon on the right by 4 so we put a 4 in front of the CO2.C4H8 + O2 --> 4CO2 + H2OWe're now going to try and balance the hydrogen by putting a 4 in front of the H2O.C4H8 + O2 --> 4CO2 +4H2OThen we're going to count the oxygens on both side and balance them by putting a 6 in front of the O2.C4H8 + 6O2 --> 4CO2 + 4H2O