Problem $7-$In a propane$-$fueled truck, $3$ percent $($by volume$)$ oxygen is measured in the exhaust stream of the running engine. Assuming "complete" combustion without dissociation, determine the air$-$fuel ratio $($mass$)$ supplied to the engine.

assume that the fuel formula $(x,y)$ is unknown, but the dry gas analysis is known from Problem $7.$ Rework the equations to determine the fuel, i$.$e$.,x,y,$ and equivalence ratio.