b) Consider the cascade of two LTI systems $S_1$ and $S_2$ shown in Fig.1(b). The impulse
responses of $S_1$ and $S_2$ are given by:
$h_1(n) = u(n)$ . and
$h_2(n) = \delta(n) - \delta(n-1)$,
respectively, where $u(n)$ is a unit-step function and $\delta(n)$ is a unit-impulse function.