Q$10)$: An SI engine burns fuel at a rate of $5\mathrm{.}4k\frac{g}{h}$ at full load, and exhaust into a closed garage of $30\mathrm{.}5$ m long, $15\mathrm{.}25$ m wide and $6\mathrm{.}1$ m high, in which the temperature is $21C$ and atmospheric pressure is $100k\frac{N}{m^2}.$ If the engine speed at full load is $1500$ rpm $,$ the fuel composition is: $84\mathrm{.}4\%C,15\mathrm{.}6\%H_2,$ and exhaust gas analysis by volume is: $13\mathrm{.}3\%C{O}_2,1\mathrm{.}3\%O_2,0\mathrm{.}6\%CO,0\mathrm{.}2\%H_2,$ find:

a$.$ the actual air$-$fuel ratio,

b$.$ how many minutes approximately will it take for the engine to produce enough CO to be lethal? $($Assume that $1$ part of CO in $100000$ parts of air by mass is dangerous to life$).$