example 6.7 p.110

#a

go = 4/(s + 4)

gc = Factor[go/(1 + go)]

gt1 = InverseLaplaceTransform[gc, s, t]

zu11 = Plot[gt1, {t, 0, 3}, PlotRange ->  {-1, 4}]

gt2 = InverseLaplaceTransform[gc/s, s, t]

zu12 = Plot[gt2, {t, 0, 5}, PlotRange ->  {0, 1}]

#b

go = 1/s  4/(s + 4)

gc = Factor[go/(1 + go)]

gt1 = InverseLaplaceTransform[gc, s, t]

zu21 = Plot[gt1, {t, 0, 3}, PlotRange ->  {-1, 3}]

gt2 = InverseLaplaceTransform[gc/s, s, t]

zu22 = Plot[gt2, {t, 0, 5}, PlotRange ->  {0, 1}]

#3 summary

Show[zu11, zu21]

Show[zu12, zu22]