A queueing system is being observed. We
A queueing system is being observed. We see that all m identical, exponential servers are busy, with n more customers waiting, and decide to shut off the arrival stream. On average, how long will it take for the system to empty completely?
题目出自Gross的Fundamentals of Queueing Theory第3版第1章，网上的答案student's solution里面没有提供这道题的答案，不知道从何下手。