Solve the following question: suppose small aircraft arrive at a certain airport according to a poisson process with rate a = 8 per hour. a. what is the probability that exactly 6 small aircraft arrive during a 1-hour period? at least 6? at least 10? b. what are the expected value and standard deviation of the number of small aircraft that arrive during a 90-min period? c. what is the probability that at least 20 small aircraft arrive during a 2.5-hour period? that at most 10 arrive during this period?