A certain gas obeys the van der Waals equation with $a=0.50 \mathrm{~m}^6 \mathrm{~Pa}$ $\mathrm{mol}^{-2}$. Its volume is found to be $5.00 \times 10^{-4} \mathrm{~m}^3 \mathrm{~mol}^{-1}$ at $273 \mathrm{~K}$ and $3.0 \mathrm{MPa}$. From this information calculate the van der Waals constant $b$. What is the compression factor for this gas at the prevailing temperature and pressure?
0.66