A non-volatile, non-electrolyte solid solute when dissolved in 40 g of a solvent, the vapour pressure of the solvent decreased from 760 mm Hg to 750 mm Hg . If the same solution boils at 320 K , then the number of moles of the solvent present in the solution is $\_\_\_\_$ . (Nearest integer) [Given: boiling point of the pure solvent $=319.5 \mathrm{~K}, \mathrm{~K}_{\mathrm{b}}$ of the solvent $=0.3 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}$ ]