A parking lot has two entrances. Cars arrive at Entrance 1 according to a Poisson Probability Distribution at an average of three per hour and at Entrance 2 according to a Poisson Probability at an average of four per hour. What is the probability that a total of three cars will arrive at the parking lot in a given hour. What is the probability that a total of three will arrive at the parking in a given hour? Assume that the numbers of cars arriving at the two entrances are independent. [Hint: This is hard but not as hard as you think].