0.5 g of a non-volatile organic substance was dissolved in 100 mL of `C""Cl_4` at `30^@C`. The vapour pressure of the solution was found to be 141.9 torr. Calculate the molar mass of the substance if the vapour pressure of `C""Cl_4` at `30^@C` is 143 torr and its density is 1.58 g `mL^(-1)`.