An operator opens the wrong valve and spills a small amount of cyclohexane $(6\mathrm{.}4lb\frac{m}{g}al,84\mathrm{.}2\frac{g}{m}ol)$ into an empty $6000$gal tank that contains air at $1$atm pressure. It is a hot day $(40C)$ and all the liquid evaporates. What is the minimum amount spilled $($L$)$ to make the entire volume of the tank flammable?