$(45$ points$)$ In the circuit below use superposition and answer the following.

a$.(20$ points$)$ Briefly, explain how the superposition principle is applied to analyze electric circuits.

b$.(25$ points$)$ Fill the following table:

$\backslash$table$[[$Variable$,$Value,Units,Points$],[l{?}^{\text{'}}($when only the $10$ V source is ON $),,$mA$,8\mathrm{.}3],[I{?}^{\text{'}\text{'}}($when only the $2$ mA source is ON$),,$mA$,8\mathrm{.}3],[$Total Ix$,,$mA$,8\mathrm{.}4]]$