Determine the average time that a snowplow is out of service

A crew of mechanics at the Department of Transportation garage make minor repairs to snowplows during the winter. The snowplows break down at an average rate of 4 vehicles per day and breakdowns are distributed according to the Poisson distribution. The mechanic can service an average of 7 vehicles per day with a repair time distribution that approximates a negative exponential distribution. Assume an 8 hour day.

A) .33 hours
B) 20 minutes
C) 2.64 hours
D) .19 days

Answer: C