Let wt. of metal oxide = 100 g

wt. of metal = 53 g

wt. of oxygen = 47 g

Equivalent weight of oxygen

                                        $\begin{array}{l}=\frac{\mathrm{wt}.\mathrm{of}\mathrm{metal}}{\mathrm{wt}.\mathrm{of}\mathrm{oxygen}}\times 8=\frac{53}{47}\times 8=9.02\\ \mathrm{Valency}=\frac{2\times \mathrm{V}.\mathrm{D}}{\mathrm{E}+35.5}=\frac{2\times 66}{9+35.5}=\frac{132}{44.5}=2.96=3\end{array}$

$\therefore$   Atomic weight = Equivalent weight x Valency

                                        = 9.20 x 3 = 27.06