A marina operates with two machines that put boats into the water. Each machine has a separate line. Boat owners arrive according to a Poisson process, and randomly choose one of the two lines to join, with the probability of choosing a particular line equal to the probability of choos- ing the other line. Once a customer enters a line, it is not possible for the customer to maneuver his/her way into the other line. Each machine operates as follows. Boat owners reverse their trailers into the machine, which op- erates like a large sling and lowers the boat into the water. The time to serve a customer at a ma- chine follows an exponential distribution. On average, a customer spends 40 minutes waiting in the line, and 10 minutes in service. In other words, a customer spends, on average, 50 minutes from entering the line till the completion of the service by a machine. a) (3 points) What is the probability that a customer can be served immediately upon his/her arrival, without waiting?