A repair service centre receives faulty or damaged computers sent in by customers, repairs them and despatches them back to the customer. Each computer is subject to the same set of tests and repair activities, and although the time taken to repair each computer will depend on the results of the tests, there is relatively little variation between individual computers. If the cycle time of the process is 12 minutes and the average work in process is four units (one at each stage of the process assuming there is no space for inventory to build up between stages), what is the throughput time of the process?