Problem $3$: Norton Equivalent of a Network $[10$ points$]$

Given the figure, please answer the following:

$($a$)[4$ points$]$ Calculate the Norton equivalent resistance $\backslash ($ R$\_\{$N$\}\backslash )$ between points $\backslash ($ a $\backslash )$ and $\backslash ($ b $\backslash ).$

$($b$)[5$ points$]$ Calculate the Norton equivalent current $\backslash ($ i$\_\{$N$\}\backslash )$ between points $\backslash ($ a $\backslash )$ and $\backslash ($ b $\backslash ).$

$($c$)[1$ points$]$ Skecth the Norton equivalent network between points a and $\backslash ($ b $\backslash ),$ showing $\backslash ($ R$\_\{\backslash$mathrm$\{$N$\}\}\backslash )$ and $\backslash ($ i$\_\{$N$\}\backslash )$ clearly.