a
(a)
$C_{\text {net }}=\frac{k+1}{2} \frac{A \varepsilon_0}{d}$
$C_{\text {net }}=\frac{A \varepsilon_0}{d-t\left(1-\frac{1}{2}\right)}=\frac{A \varepsilon_0}{d-\frac{t}{2}}$
$C_{\text {net }}=\frac{3 A \varepsilon_0}{2 d}$
$\frac{3 A \varepsilon_0}{2 d}=\frac{A \varepsilon_0}{d-\frac{t}{2}}$
