$($b$)$ Consider a hollow cylindrical that has an infinite length with an inner radius, $am$ and an outer radius, $bm$ and is placed with its axis on the $z-$axis. The cylinder has a uniform volume charge density, ${}_V\frac{C}{m^3}.$ In addition, there is also an infinite line with charge density, ${}_L\frac{C}{m}$ on the z$-$axis.

i$.$ Find the electric field intensity in all regions.

$[5$ marks$]$

ii$.$ Find the value of electric field intensity at $r=7\mathrm{.}5cm$ and $r=15cm$ if the value of inner radius, $a=5cm,$ outer radius, $b=10cm,{}_L=10n\frac{C}{m}$ and ${}_V=5\frac{C}{m^3}.$

$[2$ marks$]$