Hydrology

In Thiessen polygon method for calculating average rainfall over a watershed, three polygons have areas of $40\text{ km}^2$, $35\text{ km}^2$, and $25\text{ km}^2$ with recorded station rainfalls of $80\text{ mm}$, $60\text{ mm}$, and $50\text{ mm}$ respectively. Calculate the weighted average precipitation over the watershed in $\text{mm}$.