3. For the transfer function shown below, where R(s) and Y(s) are, respectively, the reference signal and the output signal, find all combinations of parameters ak that achieve perfect tracking. If no such combinations exist, show why this is the case. Y(s) (s+1)(s+ a) (as + 3) R(s) (s+6)(2s+a4)(s + 3) 4. Compute the sensitivity of the transfer function shown below with respect to perturbations in the plant transfer function P(s). Simplify your answer as much as possible. Try P(s)[G(s) + H(s)] 1+ P(s)H(s)F(s)