A mechanic at a local shop installs winter tires at an average rate of one car every 15minutes, according to a negative exponential distribution. Customers seeking this service arrive at the shop on the average of 1 per hour,following a Poisson distribution.The customers are served on a first-in, first-out basis and come from a large population of possible customers.What is the average time (in minutes) a customer spends in the shop (wait plus service)?