A two-node Jackson network — solving the traffic equations

Consider a system of two servers where customers from outside the system arrive at server 1 at a Poisson rate 4 and at server 2 at a Poisson rate 5. The service rates of servers 1 and 2 are respectively 8 and 10. A customer at server 1 is equally likely to join server 2 upon completion of service or leave the system. A customer at server 2, upon completion of service, goes to server 1 with probability 1/4. Then the expected number of customers in the queue waiting for service is: