A commercial propane mixture containing $80\%C_3{H}_8$ and $20\%C_4{H}_{10}$ is being used as

a fuel for a gas welding machine. In order to generate the high gas temperature

necessary for welding, the fuel is burned with an oxygen$-$enriched air consisting of

$50\%O_2$ and $50\%N_2.$ Under certain operating conditions, the flue gas contains $1\mathrm{.}0\%$

$CO$ and $5\mathrm{.}0\%O_2$ on a normal basis. Calculate the complete composition of the gas

produced and the percentage excess oxygen fed to the welding machine.