The arrivals of new telephone calls at a telephone switching office is a Poisson process N(t) with

Question:

The arrivals of new telephone calls at a telephone switching office is a Poisson process N(t) with an arrival rate of λ = 4 calls per second. An experiment consists of monitoring the switching office and recording N(t) over a 10-second interval. (a) What is PN(1)(0), the probability of no phone calls in the first second of observation?
(b) What is P N(1)(4), the probability of exactly four calls arriving in the first second of observation?
(c) What is P N(2)(2), the probability of exactly two calls arriving in the first two seconds?