Patients arrive at a hospital accident and emergency department at random at a rate of 6 per hour. (a) Find the probability that during any 90 minute period, the number of patients arriving at the hospital accident and emergency department is (i) exactly 7, (ii) at most 10. (b) A patient arrives at 11.30 a.m. Find the probability that more than one patient arrive before 11.45 a.m