The number of orders returned due to a food issue (got the order wrong, food is cold, etc.) during the lunch rush at a fast food restaurant follows a Poisson distribution with a rate of 2.4 per hour.

a. What is the probability that one hour of the lunch rush has no orders returned?

b. The lunch rush lasts two hours. What is the probability that exactly six orders are returned during the lunch rush?

c. During a one-hour period of the lunch rush, eight orders were returned. Calculate the probability that eight or more orders are returned during a one-hour period. In what fraction of one-hour periods does this event occur? (give your answer in the form 1 out of every ______.)