The correct choice is (b) {0.5 + 0.5e^-2(t-3)-e^-(t-3)} u (t-3)
For explanation I would say: Let G(s) = \(\frac{1}{s(s^2+3s+2)}\)
Or, F(s) = G(s) e^-3s
G (t) = L^-1{G(s)}
= L^-1{\(\frac{A}{s} + \frac{B}{s+2} + \frac{C}{s+1}\)}
Solving we get, A=0.5, B=0.5, C=-1
So, G (t) = 0.5 + 0.5e^-2t-e^-t
The inverse Laplace transform is F (t) = {0.5 + 0.5e^-2(t-3)-e^-(t-3)} u (t-3).