A dental clinic at which only one dentist works is open two days a week. During those two days,

A dental clinic at which only one dentist works is open two days a week. During those two days, the traffic arrivals a Poisson distribution with patients arriving at the rate of three per hour. The doctor serves patients at the rate of one every 15 minutes.What is the probability that there are one or more patients in the system?What is the probability that there are four patients in the system?What is the probability that there are four or more patients in the system?