A copper wire has a circular cross section with a radius of $1\mathrm{.}36$ mm$.$

$($a$)$

If the wire carries a current of $3\mathrm{.}73$ A$,$ find the drift speed $($in m$/$s$)$ of electrons in the wire. $($Take the density of mobile charge carriers in copper to be n $=1\mathrm{.}101029$ electrons$/$m$3.)$

$($b$)$

For the same wire size and current, find the drift speed $($in m$/$s$)$ of electrons if the wire is made of aluminum with n $=2\mathrm{.}111029$ electrons$/$m$3.$