A Private Branch Exchange (PBX) with M/M/3/20/4 accepts 1 call per minute with a holding time of 2 minutes per call. This PBX is using the Engset model for the operation.

i) Calculate the offered traffic per idle source and offered traffic per source for the PBX system. 

ii) Compute the Blocking Probability of the PBX and state the number of customers that will get immediate service.

iii) If one of the customers is no longer served by the system, calculate the time congestion.

iv) Set up the complete state transition diagram of the PBX.