At $25^{\circ} \mathrm{C}$, the percentage of ionisation of ' $x$ ' M acetic acid is 4.242 . What is the value of $x$ ? $\left(K_{\mathrm{a}}=1.8 \times 10^{-5}\right)$

At $25^{\circ} \mathrm{C}$, the percentage of ionisation of $x \mathrm{M}$ acetic acid is 4.242 . What is the pH of the acetic acid solution?

$$ \begin{aligned} & (\log 4.242=0.6275) ;(\log 0.04242=-1.372) \\ & \left(K_{\mathrm{a}}=1.8 \times 10^{-5}\right) \end{aligned} $$

At $T(\mathrm{~K})$, the solubility product of AgBr is $4 \times 10^{-13}$. What is its solubility in 0.1 M KBr solution?