A parallel-plate capacitor consists of two conducting plates, each of area \(A\), separated by a distance \(d\). The region between the plates is filled with a dielectric material whose dielectric constant varies continuously with distance \(y\) from the bottom plate (\(y = 0\)) to the top plate (\(y = d\)) according to \(\kappa(y) = \kappa_0 \left(1 + \dfrac{y}{d}\right)\), where \(\kappa_0\) is a positive constant. Which of the following is a correct expression for the total capacitance \(C\) of this capacitor?