A natural gas has the following ultimate analysis by mass: H2, 23.3%; C, 74.72%; N2, 0.76%; and O2, 1.22%. The flue gases have the following volumetric analysis: H2O, 15.583%; CO2, 8.387%; O2, 3.225%, N2, 72.805%. Calculate (a) the percent theoretical air used in combustion, and (b) the dew point if the flue gases are at 2 bar.