$\varepsilon(x)=\varepsilon_{0}+k x, \text { for }\left(0\,<\,x \leq \frac{d}{2}\right)$
$\varepsilon(x)=\varepsilon_{0}+k(d-x)$, for $\left(\frac{d}{2} \leq x \leq d\right)$
\(dC =\frac{\left(\varepsilon_{0}+ kx \right) A }{ dx }\)
Capacitance of half of the capacitor
\(\frac{1}{C}=\int_{0}^{ d / 2} \frac{1}{ dc }=\frac{1}{ A } \int_{0}^{ d / 2} \frac{ dx }{\varepsilon_{0}+ kx }\)
\(\frac{1}{ C }=\frac{1}{ kA } \ln \left(\frac{\varepsilon_{0}+ kd / 2}{\varepsilon_{0}}\right)\)
Capacitance of second half will be same
\(C _{\text {eq }}=\frac{ C }{2}=\frac{ kA }{2 \ln \left(\frac{2 \varepsilon_{0}+ kd }{2 \varepsilon_{0}}\right)}\)