Liquid Solution

Benzoic acid undergoes dimerisation in benzene. $x \mathrm{~g}$ of benzoic acid (molar mass $122 \mathrm{~g} \mathrm{~mol}^{-1}$ ) is dissolved in 49 g of benzene. The depression in freezing point is 1.12 K . If degree of association of acid is $88 \%$. What is the value of $x$ ? $\left(K_f\right.$ for benzene $\left.=4.9 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}\right)$