Benzene's been under a lot of pressure lately

$39\text{ grams}$ of pure benzene at a certain temperature is taken in a container. The vapor pressure of benzene at this temperature is $0.850 \text{ bar}$ . To this, a non-volatile, non-electrolyte solid solute weighing $0.5 \text{ grams}$ is added. The vapor pressure of the solution is then $0.845 \text{ bar}$

What is the molecular mass of the solid substance (in grams per mole) ?

Details

• $\text{1 bar = 0.987 atm}$
• $\text{Molecular formula of benzene is } C_6H_6$