$4.$ Test the above systems in problems $2$a$,2$b$,2$c for shift$-$invariance using the test procedure given in class and determine whether they are shift$-$invariant or not shift$-$invariant.Test the following systems for linearity using the test procedure given in class and determine

whether they are linear or non$-$linear.

a$.$ y$[$n$]=2$x$[$n$]+1$

b$.$ y$[$n$]=(1)/(2)$x$[$n$]-(1)/(4)$x$[$n$-1]$

c$.$ y$[$n$]=$x$[2$n$]$