It is time for students to register for classes, and a line is forming at the registrar's office for those who need assistance. It takes the registrar an exponentially distributed amount of time to service each student, on average 4 minutes. Students arrive at the office and get in line according to a Poisson process at the rate of one student every 6 minutes. The arrival times of the students are independent of the registrar's service time. (a) What is the long-term probability that there are not more than 3 students at the registrar's office? (b) How long, on average in the long run, is a student at the registar's office? (c) What is the long-term expected number of students at the registar's office waiting to be served by the registrar?