Gotham Township has 5 police cars. The police department receives two types of calls:

emergency (type 1) and nonemergency (type 2) calls. Interarrival times for each type of call are exponentially distributed, with an average of 10 emergency and 20 nonemergency calls being received each hour. Each type of call has an exponential service time, with a mean of 8 minutes (assume that, on the average, 6 of the 8 minutes is the travel time from the police station to the call and back to the station). Emergency calls are given priority over nonemergency calls. On the average, how much time will elapse between the placement of a nonemergency call and the arrival of a police car?