Three parallel plate air capacitors are connected in parallel. Each capacitor has plate area $\frac{{ }^{}{A}^{}}{3}$ and the separation between the plates is $d^{}, 2d^{} \mathrm{a}\mathrm{n}\mathrm{d} 3d^{}$ respectively. The equivalent capacity of combination is (${\epsilon }_0=$ absolute permittivity of free space)