Ionic Equilibrum

The percentage of ionisation of 1 L of $x \mathrm{M}$ acetic acid is 4.242 and is called solution " $A$ ". The percentage of ionisation of 1 L of $y \mathrm{M}$ acetic acid is 3 and is called solution " $B$ ". Solution " $A$ " is mixed with solution " $B$ ". What is the concentration of acetic acid in the resultant solution? ( $K_{\mathrm{a}}$ of acetic acid $=1.8 \times 10^{-5}$ )