Arrivals of the Number X metro bus form a Poisson process with rate one bus per hour, and arrivals of the Number Y bus form an independent Poisson process of rate seven buses per hour. (2.1) What is the probability that exactly three buses pass by in one hour? (2.2) What is the probability that exactly three Number Y buses pass by while you are waiting for a Number X bus? (2.3) When the maintenance depot goes on strike, half the buses break down before they reach your stop. What then is the probability that you wait for 30 minutes without seeing a single bus