3. A digital control system identical to that depicted in the lecture note consists of a zeroorder hold, process mode Gm(s)=s+22, disturbance model Gd(s)=s+21, sampling time T=1 and a proportional controller. (a) what are the values of proportional gain that stabilize this control system? (b) Will the alarm go off at t=T if its threshold is 0.5 and a unit step change occurs in the disturbance variable d(s) at t=0 ? (30 Marks)