Let the atomic mass of metal, 'M' = a
Given, equivalent mass of metal, M = E
$xM + y O \rightarrow M_x O_y$
$\therefore $ 'xa' g metal 'M' reacts with oxygen = 16y g,
According to law of chemical equivalents $ w \propto E$
$\frac{w_1}{w_2} = \frac{E_1}{E_2}$
$\frac{xa}{16y} =\frac{E}{8}$
$a = 2E \left( \frac{y}{x} \right)$