A mixture of 25% hydrogen and 75% propane is burned with the 25% excess air. Fractional conversions of 85% of the hydrogen and 90% of the propane are achieved; of the propane that reacts, 95% reacts to produce the CO2 and the balance reacts to produce the CO. The hot combustion product gas passes through a boiler in which heat transferred from the gas converts boiler feed water into the steam. Determine the concentration of CO (ppm) in the stack gas