Two people who prepare tax forms are working in a store at a local mall. Each has a chair next to his desk where customers can sit and be served. In addition there is one chair where customers can sit and wait. Customers arrive at rate 

but will go away if there is already someone sitting in the chair waiting. Suppose that server i requires an exponential amount of time with rate i and that when both servers are free an arriving customer is equally likely to choose either one.

(a) Formulate a Markov chain model for this system with state space f0; 1; 2; 12; 3g where the first four states indicate the servers that are busy while the last indicates that there is a total of three customers in the system: one at each server and one waiting.

(b) Consider the special case in which  D 2;1 D 3 and 2 D 3. Find the stationary distribution.