15. The federal government is undertaking a massive process analysis of the notoriously chaotic border San Diego and Tijuana. They have selected the San Ysidro station as a sample case and would like your input in doing the following analysis. Automobiles arrive from Mexico at the rate of20 per houraccording to a Poisson distribution. The station has3 inspection lanes for carsand1 inspection lane for trucks. All cars join a common queue and go to the first available car inspection lane. About30%of the incoming vehicles are trucks and the remaining are cars. Average inspection time for a truck is5 minand average inspection time for a car is6 min.

Also, authorities have noticed that about50%of the trucks and25%of the incoming cars need further scrutiny of contents and documents. For this, they are diverted to a separate lane in the San Diego side of the border, where it takes about8 min per vehicleto get checked thoroughly. This single "close scrutiny" lane is designed to handle both cars and trucks. For your convenience, a simple representation of the system is shown below.

Suppose inspection times at all stages are distributed exponentially. Answer the following question regarding the flow of vehicles through this Border Station.

What is the average time spent by a vehicle en route to San Diego at this border station? Give your answer in minutes.