Answer:
4 minutes
Step-by-step explanation:
Availability
time = 60 minutes
Capacity = 15 cars per hour
Time taken for each car to serve = 60 / 15 minutes = 4 minutes
Arrival of car
Cars per hour = 10 cars
Time taken by each car = 60 / 10 = 6 minutes per car
As cars are arriving later than the time taken to serve each so the average time in line will be 4 minutes