A generator system consists of a primary and a standby unit. the primary fails at a constant rate of 2 per manth, the standby unit fails only when on-line at a constant rate of 4 per month, Repair can begin only when both units have failed. both units are repaired at the same time of 20 days (2/3 month). derive the steady sate equations for the state probabilities and solve for the system availability?