Benzene and toulene form an ideal solution. $3$ $\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{e}$ benzene and $2$ $\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{e}$ toulene are added. V.P. of pure benzene and toulene are $300$ $\&$ $200$ $\mathrm{m}\mathrm{m}$ of $\mathrm{H}\mathrm{g}$ respectively. The V.P. of the solution (in mm of $\mathrm{H}\mathrm{g}$) is