$4-$ A communication system is using PAM to transmit a three$-$character message $"$H$20".$

After converting each character in the message into its $7-$bit ASCII representation and

interpreting it as a two's complement representation, we see that the three symbols

corresponds to three decimal numbers: $-56,50,-49.$ These numbers are denoted by $[0],$

m$[1],$ and m$[2],$ respectively. Assume $[$n$]=0$ for other values of n$.$

Recall that the PAM signal is constructed from the discrete$-$time message $[$n$]$ via

$00$

XPAM$($t$)=$

m$[$n$]$p$($t$-$nT$3).$

$7$L $=-00$

a$.$ Plot XpAM$($t$)$ when the following pulse is used and T $=1$

b$.$ Plot xPAM$($t$)$ when the following pulse is used and Ts $=0\mathrm{.}4.$