$I=n e A v$

Where I = current

$\mathrm{n}=$ charge carrier current density

$\mathrm{e}=$ charge on the carriers

$A=$ cross sectional area

$\mathrm{v}=$ drift velocity

In the above example

$l=$ current $=\mathrm{i}$

$\mathrm{n}=$ charge carrier current density $=\mathrm{p}$

$\mathrm{e}=$ charge on the carriers $=\mathrm{q}$

$A=$ cross sectional area $=s$

$\mathrm{v}=$ drift velocity $=\mathrm{v}$

hence $i=p q s v$

$\therefore v=\frac{i}{p q{s}}$