[tex]md = 36 \: g \: cauciuc \\ \\ ms = md + m_{solvent} = > m_{prenandez} = m_{cauciuc} + m_{benzen} \\ \\ c = \frac{md \times 100}{ms} \\ \\ \frac{9}{100} = \frac{36}{(36 + m _{benzen)}} \\ \\ m_{benzen} = 364 \: g \\ \\ m_{prenandez} = 36 + 364 = 400 \: g [/tex]