Asmall post office has two open windows customers arrive according to a poisson distribution at the rate of 1 every 3 minutes . however only 80% of...

Asmall post office has two open windows customers arrive according to a poisson distribution at the rate of 1 every 3 minutes . however only 80% of them seek service at the windows. the service time per customer is exponential with amean of 5 minutes. all arriving customers form a line and access available windows on a FCFS basis.(i)what is the probability that an arriving customer will wait in a line (ii)what is the probability that both windows are idle?(iii) what is the average length of the waiting line?