A pizza parlor serves n different types of pizza, and is visited by a number k of customers in a given period of time, where k is a poisson random variable with mean
a.
Sorry I do not know the answer, because you don't tell how many types of pizza there is. You also don't tell how many customers there are. You have to at least tell us at least one of the numbers. To make it easier for us to solve it for you.