Chem problem - liters of gas formed from this reaction

Please help me with the following chem. Problem. It is driving me nuts because I don’t think it applies to any of the gas laws and I know it can be solved with some sort of molar conversion but I don’t know how to set it up.
If 10.5 liters of CH4 reacts with 2.5 liters of oxygen, how many liters of CO2 are formed?
CH4 + O2 -> H2O + CO2

We need to make a few assumptions here, which I'll explain later on.

First you need to convert volume to moles of gas. One mole of an "ideal" gas occupies 24 litres at room temperature and pressure (RTP). Therefore 10.5/24 moles of methane and 2.5/24 moles of oxygen are reacting in this case. That's the equivalent of 0.4375 moles of methane and 0.104 moles of oxygen.

As there is less oxygen, that will limit the amount of carbon dioxide that can be produced. You would actually get 1 mole equivalent (0.104 moles) of carbon dioxide produced in this case.

0.104 moles of carbon dioxide at RTP would occupy 2.5 litres (same as the oxygen you started with).

Assumptions:
- Gas is behaving "ideally". In the real world it doesn't, but this approximation is fine in most cases.
- Reaction is taking place at RTP. In the real world it wouldn't. We usually heat these things to get them going.