a$)$ A digital signal $($n$)$ is defined as a$($n$)=4[$u$($n$)-($n $-3)]+2[$u$($n $-2)-$ un $-7)].$ Calculate the signal y$($n$)=$ a$(-2$n $+3)$ by direct method, represent the signal insequence form and sketch the signal.$(15$ Marks$)$b$)$ A discrete T system has an unit sample response of h$($n$)=5($;$)"($n$)-4($;$)"-)$u$($n$)$and the input to the system is x $($n$)=10\mathrm{.}5$n $20$elseDetermine the output response y$($n$)$ of the system using convolution sum.