A mixture of propane (75 mol%) and hydrogen are burned with 25% excess air. Fractional conversions of 95% of the propane and 80% of the hydrogen are achieved; of the propane that reacts, 90% reacts to form CO2 and the balance reacts to form CO. The hot combustion product gas passes through a boiler in which heat transferred from the gas converts the boiler feedwater to steam. Calculate the concentration of CO (ppm) in the stack gas.