$3.$ Acetone has a TLV of $500$ ppm$,$ and the molecular weight is $58\mathrm{.}05,$ and the specific gravity is $0\mathrm{.}785.$ Toluene has a TLV of $50$ ppm$,$ and the molecular weight is $92\mathrm{.}13,$ and the specific gravity is $0\mathrm{.}865.$ An open tank has a mixture of acetone and toluene both evaporating into the room at the rate of $0\mathrm{.}005$ pints$/$min and $0\mathrm{.}000278$ respectively. The room has a volume of $1000$ cubic feet, and the mixing factor is $3.$ There is an $18$ inch diameter duct supplying air to the room. What is the required airflow to keep the overall concentration at the TLV$??????$