Vapour pressure of `C_6H_6` and `C_7H_8` mixture at `50^@C` is given P (mm Hg) = `180X_B + 90`, where `X_B` is the mole fraction of `C_6H_6`. A solution is prepared by mixing 936 g benzene and 736 g toluene and if vapours over this solution are removed and condensed into liquid and again brought to the temperature `50^@C`, what would be mole fraction of `C_6H_6` in the vapour state. (At. wt. of C 12, H = 1)