CH4 + __O2 → CO2 + ___H2O

balance this equation

CH4+2O2→CO2+2H2O

Explanation:

Start with the least common atoms and leave things like H and O to the end.

You need to have the same number of methane reactants as carbon dioxide products because there is one carbon in each. I’ll set them both to 1 for now. O see two things with oxygen on the product side so we will have to juggle numbers a bit to figure out those. There is only H in the water so we’ll go there next. One CH4 gives 2 water molecules so we have that done now. At last we can tackle the O atoms. In two waters there are 2 and in the CO2 there are two more so a total of 4 O atoms in the products so we need two O2 molecules in the reactant side.

Hope this is useful.