CH4 + 2O2 → CO2 + 2H2O

Here's how to balance it:

1. Count the atoms on each side:

- Reactants: 1 C, 4 H, 4 O

- Products: 1 C, 2 H, 3 O

2. Balance the carbons: The carbons are already balanced.

3. Balance the hydrogens: There are 4 H on the reactant side and only 2 on the product side. Add a coefficient of 2 in front of H2O:

- CH4 + 2O2 → CO2 + 2H2O

4. Balance the oxygens: Now there are 4 O on the reactant side and 4 O on the product side. The equation is balanced.