Let a mL, b mL and c mL be volumes of C3H8, CH4 and CO respectively in 100 mL given simple, then
a + b + c = 100 and a = 36.5
Now CO2 is formed as a result of combustion of mixture.
∴ Vol. of CO2 formed = 3a + b + c = 3 x 36.5 + (100 - 36.5) = 173 mL