$[12]$ A laboratory hood has ventilation face velocity of $110f\frac{t}{m}in$ traveling through the opening

which is $70$ inches wide and $15$ inches high. Acetone at $23C$ is spilled on the bench top inside the

hood. The area of the spill is $70$ inches by $24$ inches. Assuming the hood has excellent mixing $(k$

$=0\mathrm{.}5$ what is the concentration of acetone in the hood in $ppm?($Please answer the question with full solving and a clear way$)$