Help me to solve this problem (Markov chain)

Hi

I'm trying to solve the following question but I'm somehow confused. I know how to solve it for two parallel server but for a combination of series and parallel I don't know what should I do...

Arrivals to a 3 server system are according to a Poisson process with rate λ. Arrivals

finding server 1 free enter service with 1. Arrivals finding 1 busy but 2 free enter

service with 2. Arrivals finding both 1 and 2 busy do not join the system. After

completion of service at either 1 or 2 the customer will then either go to server 3 if

3 is free or depart the system if 3 is busy. After service at 3 customers depart the

system. The service times at i are exponential with rate μi, i = 1, 2, 3.

(a) Define states to analyze the above system.

(b) Give the balance equations. Do not attempt to solve.

(c) In terms of the solution of the balance equations, what is the average time that

an entering customer spends in the system?

(d)what is the probability that a customer who arrives when the system

is empty is served by server 3?

Thank you for your help in advance!