In the figure a capacitor is filled with dielectrics K₁ = 2, K₂ = 3, K₃ = 6 and $\frac{{\mathrm{\epsilon }}_0\mathrm{A}}{\mathrm{d}}$  = C. The resultant capacitance between P and Q is

$\begin{array}{r}{\mathrm{C}}_1=\frac{{\mathrm{K}}_1{\mathrm{ϵ}}_{\mathrm{o}}\mathrm{A}/2}{\mathrm{d}/2}\\ {\mathrm{C}}_2=\frac{{\mathrm{K}}_2{\mathrm{ϵ}}_0\mathrm{A}/2}{\mathrm{d}}\\ {\mathrm{C}}_3=\frac{{\mathrm{K}}_3{\mathrm{ϵ}}_{\mathrm{o}}\mathrm{A}/2}{\mathrm{d}/2}\end{array}$
C₁ and C₃ are in series and this combination is in parallel combination with C₂ 

$C_{eq}=\frac{\mathrm{A}{\epsilon }_q}{ \mathrm{d}}\left[\frac{{\mathrm{k}}_2}{2}+\frac{{\mathrm{k}}_1{\mathrm{k}}_3}{{\mathrm{k}}_1+{\mathrm{k}}_3}\right]$

On putting the values we get C_eq=3C