$10\text{ g}$ of a non-volatile solute is dissolved in $200\text{ g}$ of water to make a solution. It has a vapour pressure of $31\cdot84\text{ mm Hg}$ at $308\text{ K}$. Calculate the molar mass of the solute. [Given : Vapour pressure of pure water at $308\text{ K} = 32\text{ mm Hg}$]