So first we need to know what the formulas are:
Methane: [tex] CH_{4} [/tex]
Oxygen: [tex] O_{2} [/tex]
Carbon Dioxide: [tex] CO_{2} [/tex]
Water: [tex] H_{2}O [/tex]
So then we follow the equation as specified in the question. Note that it does not need to be balanced, as the question states it wants the unbalanced equation:
[tex] CH_{4}+O_{2} [/tex] → [tex] CO_{2}+H_{2}O [/tex]
This is the preliminary, unbalanced equation with the correct chemical formulas.