Six identical conducting plates of area A each are connected as shown. The separation ‘d’ between any two adjescent plates is same. ${\mathrm{\epsilon }}_0$ is permittivity of free space between the plates. The effective capacitance between the terminals of battery is $\frac{3\mathrm{k}{\in }_{\mathrm{o}}\mathrm{A}}{2\mathrm{d}}$. The value of ‘k’ is