A natural gas contains $85$ mol$\%$ methane $(C{H}_4)$ and the remaining ethane $(C_2{H}_6)$ being burned in the presence of air.

a$.$ Sketch and label the flow diagram for the process and write the stoichiometric equations for the above combustion process.

$(5$ marks$)$

b$.$ Calculate the amount of theoretical oxygen required if all of the methane and ethane is completely burned and determine the amount of air supplied if this fuel is to be burned with $125\%$ excess air.

$(8$ marks$)$

c$.$ Determine the flow rate of the product gas in $mo\frac{l}{h}.$

$(4$ marks$)$