A local law agency claims that the number of times a patrol car passes through a particular neighbourhood follows a Poisson Distribution with a mean of four time per nightly shift. Let x denote the number of times that a patrol car passes through the neighbourhood during a nightly shift. a. Calculate the probability that two patrol cars pass through the neighbourhood during a nightly shift. b. Assuming that nightly shifts are independent and assuming that the agency's claim is correct, find the probability that exactly one patrol car will pass through the neighbourhood on each of three consecutive nights.