The sulphate of a divalent element contains 42.2% element. The equivalent mass would be

Equivalent mass of ${\mathrm{SO}}_4^{2-}$ is:

$\mathrm{Equivalent} \mathrm{mass}=\frac{32+64}{2}=48$

Percentage of ${\mathrm{SO}}_4^{2-}$ is $57.8\% \left(100-42.2\%\right).$

Assume that equivalent mass of compound is a. Then the value of a is calculated as:

$$\begin{gathered} \mathrm{a}\times 57.8\%=48 \\ \mathrm{a}=83.04 \end{gathered}$$

Equivalent mass of element is calculated as:

$$\begin{gathered} \mathrm{Equivalent} \mathrm{element} \mathrm{mass}=\mathrm{Equivalent} \mathrm{mass} \mathrm{of} \mathrm{compound}-\mathrm{Equivalent} \mathrm{mass} \mathrm{of} \mathrm{sulphate} \\ \mathrm{Equivalent} \mathrm{element} \mathrm{mass}=83.04-48=35.0 \end{gathered}$$