Evaporation and Drying

Air at standard atmospheric pressure ($101.325\text{ kPa}$) has a dry bulb temperature of $30^\circ\text{C}$ and partial pressure of water vapor $p_v = 2.50\text{ kPa}$. Using the humidity ratio formula $W = 0.622 \frac{p_v}{P - p_v}$, the humidity ratio in $\text{kg water / kg dry air}$ is ________ (round off to 4 decimal places).