Over a $30$ m length of $150$ mm vacuum line carrying air at $293$ K $($Molecular Weight $=26\mathrm{.}44$ kg$/$kmol$,$ Viscosity $=18\mathrm{.}12*10^-6$ N s$/$m$^2),$ the pressure falls from $1$ kN$/$m$^2$ to $0\mathrm{.}1$ kN$/$m$^2.$ If the relative roughness e$/$d is $0\mathrm{.}002,$ what is the approximate mass flow rate? $($unit is required$).$