how can we solve part C?

Consider the feedback control system with the following transfer functions: Gp=Gd=6s+11,Gm=2s+11,Gv=3s+11andGc=kc A. If a unit step change in the set point is applied, show that the closedloop system produces unstable responses when the controller gain Kc is too large (simulate with different values of Kc ). B. Analytically obtain the mathematical expression of y(t) C. Determine the value of Kc that makes the system critically stable