E$7)$ A propane gas $(C_3{H}_8)$ direct$-$fired batch heat treating oven is required to maintain a $CO$ concentration in the oven at $2\mathrm{.}0\%CO$ by mass $($of total product mass$)$ during heating operations. This is to ensure the oven environment is neither excessively oxidizin nor de$-$carburizing. Determine the associated "theoretical air", $,$ of the process along with the related balanced equation.