A stream of butane (C4H10) at 168 kg/hr is burned in a boiler to heat water. The boiler is fed 16 % XS air. What is the composition of O2 in the flue gas, in mass percent (dry basis) ? Use 3 decimal digits in your answer Air can be treated to be 78 % N2, 21 % O2 and 1% Ar, where all percentages are in mole percent. The average molecular weight for air of this composition is 28.970 kg/kgmol