The number of telephone calls that arrive at a exchange is often modeled as a Poisson random

Question:

The number of telephone calls that arrive at a exchange is often modeled as a Poisson random variable. Assume that on the average there are 10 calls per hour.
(a) What is the probability that there are exactly 5 calls hour?
(b) What is the probability that there are 3 or less calls hour?
(c) What is the probability that there are exactly 15 two hours?
(d) What is the probability that there are exactly 530 minutes?