Arrivals at a walk-in optometry department in a shopping mall have been found to be Poisson distributed

Question:

Arrivals at a walk-in optometry department in a shopping mall have been found to be Poisson distributed with a mean of 2.5 potential customers arriving per hour. If x 5 number of arrivals during a given hour, determine the following:
a. E(x)
b. P(x = 1)
c. P(x = 3)
d. P(x ≤ 5)
e. P(2 ≤ x ≤ 6)