A local bar keeps records of Happy Hour (5: to 6:00 PM), number of customers arriving. On average, 7 customers arriving during the happy hour.

A local bar keeps records of Happy Hour (5:00 P.M. to 6:00 PM), number of customers arriving. On average, 7 customers arriving during the happy hour. Let's assume these arrivals follow the Poisson distribution. On a given day, what is probability of at most 2 customers will arrive during the Happy Hour?