SOLUTIONThe multiple-server model for s = 4, m = 1, and l = 3 is appropriate. To find the total cost of labor and idle trucks, we must calculate the average number of trucks in the system at all times. Figure B.5 shows the results for the American Parcel Service problem using the Waiting-Lines Solver from OM Explorer. The results show that the four-bay design will be utilized 75 percent of the time and that the average number of trucks either being serviced or waiting in line is 4.53 trucks. That is, on average at any point in time, we have 4.53 idle trucks. We can now calculate the hourly costs of labor and idle trucks: