c
$\frac{\varepsilon_{\mathrm{o}} \mathrm{A}}{\mathrm{d}}=9 \mathrm{\,PF}$
$\mathrm{C}^{\prime}=\frac{\frac{\varepsilon_{\mathrm{o}} \times 3 \mathrm{A}}{\mathrm{d} / 3} \times \frac{\varepsilon_{\mathrm{o}} \times 6 \mathrm{A}}{2 \mathrm{d} / 3}}{\frac{\varepsilon_{\mathrm{o}} \times 3 \mathrm{A}}{\mathrm{d} / 3}+\frac{\varepsilon_{\mathrm{o}} \times 6 \mathrm{A}}{2 \mathrm{d} / 3}}=\frac{\frac{9 \varepsilon_{\mathrm{o}} \mathrm{A}}{\mathrm{d}} \times \frac{9 \varepsilon_{\mathrm{o}} \mathrm{A}}{2 \mathrm{d}}}{\frac{18 \varepsilon_{\mathrm{o}} \mathrm{A}}{2 \mathrm{d}}}=\frac{9}{2} \frac{\varepsilon_{\mathrm{o}} \mathrm{A}}{\mathrm{d}}$
$C^{\prime}=\left(\frac{9}{2} \times 9\right) \,p F=40.5 \,p F$