One kmol of ethane (C2H6) is burned with an unknown amount of air during a combustion process.

Question:

One kmol of ethane (C2H6) is burned with an unknown amount of air during a combustion process. An analysis of the combustion products reveals that the combustion is complete, and there are 3 kmol of free O2 in the products. Determine
(a) The air-fuel ratio
(b) The percentage of theoretical air used during this process.