A steady current is passing through a linear conductor of nonuniform cross-section. The drift velocity of electrons

The quantity of charge passing through any cross-section per second is nothing but the current flowing in the conductor.

As given, the current is a steady current, which means the current is uniform throughout the cross-section. 

$\mathrm{i}={\mathrm{neAv}}_{\mathrm{d}}$

$\mathrm{As} \mathrm{i} \mathrm{is} \mathrm{constant} \mathrm{n} \mathrm{and} \mathrm{e} \mathrm{are} \mathrm{also} \mathrm{constant}$

${\mathrm{v}}_{\mathrm{d}}\propto \frac{1}{\mathrm{A}}$