$K_{a}=1.5 \times 10^{-5} \ldots \ldots .(i)$

$H C N \rightleftharpoons H^{+}+C N^{-}, K_{a 1}=4.5 \times 10^{-6} \ldots \ldots(i i)$

For $\mathrm{CN}^{-}+\mathrm{CH}_{3} \mathrm{COOH} \rightleftharpoons \mathrm{HCN}+\mathrm{CH}_{3} \mathrm{COO}^{-}$

$K=?$

On subtracting Eq. $(ii)$ from Eq. $(i)$, we get

$\mathrm{CH}_{3} \mathrm{COOH}+\mathrm{CN}^{-} \rightleftharpoons \mathrm{HCN}+\mathrm{CH}_{3} \mathrm{COO}^{-}$

$k=\frac{K_{e}}{K_{a_{1}}}=\frac{1.5 \times 10^{-5}}{4.5 \times 10^{-10}}$

$=\frac{10^{5}}{3}=3.33 \times 10^{4}$

$\approx 3 \times 10^{4}$