c
At steady state, no current through the capacitor hence
current in circuit $=\frac{12}{8}=\frac{3}{2} \mathrm{\,A}$
$\mathrm{V}_{\mathrm{A}}-\mathrm{V}_{\mathrm{B}}=9 \mathrm{V}$
$\mathrm{q}=\mathrm{C}\left(\mathrm{V}_{\mathrm{A}}-\mathrm{V}_{\mathrm{B}}\right)$
$=2 \times 9=18\, \mu \mathrm{C}$
