The port of Trop can service only 1 ship at a time. However, there is mooring space for 3 more ships. Trop is a favorite port of call, but, if no mooring space is available the ships have to go to the next port. An average of 7 ships arrive each week, according to the Poisson process. The Port of Trop has the capacity to handle an average of 8 ships a week, with service times exponentially distributed. What is the expected number of ships waiting or in service at the Port of Trop?