A gaseous mixture containing 80 mol% methane and the balance methyl ethyl ketone (C4H8O) is burned with 50% excess air. During the reaction, 95% of the methane and 75% of the methyl ethyl ketone were burned; however, some of the methane that burns forms CO. The exhaust gas contains 0.5 mol% CO on a dry basis. On the basis of 1 mol of hydrocar- bon gas, calculate the moles of oxygen in the exhaust gas.