Molar volume ( $V_m$ ) of a van der Waals gas can be calculated by expressing the van der Waals equation as a cubic equation with $V_m$ as the variable. The ratio (in $m o l d m^{-3}$ ) of the coefficient of $V_m^2$ to the coefficient of $V_m$ for a gas having van der Waals constants $a=6.0 \mathrm{dm}^6 \mathrm{atmmol}^{-2}$ and $b=0.060 \mathrm{dm}^3 \mathrm{~mol}^{-1}$ at 300 K and 300 atm is $\_\_\_\_$
Use: Universal gas constant $(R)=0.082 \mathrm{dm}^3 \mathrm{atmmol}^{-1} \mathrm{~K}^{-1}$