A fast food restaurant wants to determine if it is feasible…

A fast food restaurant wants to determine if it is feasible to stay open during the hours between 1 am and 4 am.  Data was collected over a period of several weeks and on average there were 3.2 customers per hour during those overnight hours. Assuming the number of customers arriving follows a Poisson distribution, what is the probability that there will be exactly 5 customers arriving during the three hours between 1 am and 4 am