An electric manufactures high-voltage switches and other equipment for electric utilities. One line that is staffed by three workers assembles a particular type of switch. Currently the threes workers have fixed assignments; each worker fastens a specific set of components on the switch and passes it downstream on a rolling conveyor. The conveyor has capacity to allow a queue to build up in front of each worker. The bottleneck is the middle station with a rate of 11 switches per hour. The raw processing time is 15 minutes. To improve efficiency of the line, management is considering cross-training the workers and implementing some form of flexible labor system.

1. What is the critical amount of WIP that is needed by this line?