Question

A mole of methane reacts with 64g of oxygen at 1 atm, 425 K. There are two ways in which methane can react with oxygen. It can either form water vapor and carbon dioxide or water vapor and carbon monoxide. After reaction the final gas density is 0.7282 g/L.

What is the fraction of methane that reacted to produce CO2? What is the fraction of methane that reacted to produce CO?
(Assume that methane is fully reacted)

Can someone just guide me in the right direction?

Here's what I have so far:
64g O2 --> 2 mol O2
CH4 + 2 O2 --> 2 H2O + CO2
2 CH4 + 3 O2 --> 4 H20 + 2 CO