Molecules of benzoic acid ($C_6{H}_{5}COOH$) dimerise in benzene. $\text{'}w\text{'}$ g of the acid dissolved in $30 g$ of benzene shows a depression in freezing point equal to $2 K$. If the percentage association of the acid to form dimer in the solution  is 80, then w is

(Given that $K_f=5K\mathrm{kg}{\mathrm{mol}}^{-1}$, Molar mass of benzoic $acid=122g mo{l}^{-1}$)