When of oxalic acetic acid is dissolved in of benzene, the freezing point of the solution is…

When $0\cdot4\text{ g}$ of oxalic acetic acid is dissolved in $40\text{ g}$ of benzene, the freezing point of the solution is lowered by $0\cdot45\text{ K}$. Calculate the degree of association of acetic acid. Acetic acid forms dimer when dissolved in benzene. ($K_f\text{ for benzene} = 5\cdot12\text{ K kg mol}^{-1}, \text{at. wt. C} = 12, \text{H} = 1, \text{O} = 16$)