Carbon dioxide can be made to react with hydrogen gas to produce methane and water vapour, here is an example.

CO2 + H2 --> CH4 + H2O
CO2 + 3H2 --> CH4 + H2O
CO2 + 3 H2 --> CH4 + 2H2O
CO2 + H2 --> CH4 + H2O
CO2 + H2 --> CH4 + 2H2O
CO2 + 4H2 --> CH4 + 2 H2O

Now the equation is balanced because every element has equal subscripts, so there is the same amount on the both sides.