\\\\(Q_A=C_A\\ V_A\\\\)\\\\(=2\ imes 10^{-6}\ imes 12\\\\)\\\\(Q_A=24\ imes 10^{-6}\\\\)\\\\(Q_B=C_B\\ V_B\\\\)\\\\(=4\ imes 10^{-6}\ imes 6\\\\)\\\\(Q_B=24\ imes 10^{-6}\\\\)Now when plates are attached total charge \\\\(=Q_A+Q_B\\\\)\\\\(Q=48\ imes 10^{-6}C\\\\)Let x he charge on A then Q-x charge is on B\\\\( \\Rightarrow x=2\\mu F\ imes V\\ and\\ Q-x=4\\mu \\ F\ imes V.\\\\)\\\\( \\Rightarrow \\frac{x}{Q-x}=\\frac{1}{2}\\ \\ \\ 2x=Q-x\\ \\ \\ \\ x=\\frac{9}{3}\\\\)\\\\(x=16\ imes 10^{-6};Q-x=32\ imes 10^{-6}\\\\)Now charge flows from A to B is given by,\\\\(=final -initial\\\\)\\\\(=32\ imes 10^{-6}-20\ imes 10^{-6}\\\\)\\\\( \\bigtriangleup Q=8\ imes 10^{-6} C\\\\)\\\\(\\bigtriangleup Q = 8\\mu C\\\\)