A supplier of instrument gauge clusters uses a kanban system to control material flow. The gauge cluster housings are transported six at a time. A fabrication center produces approximately 18 gauges per hour. It takes approximately two hours for the housing to be replenished. Due to variations in processing times, management has decided to keep 10 percent of the needed inventory as safety stock. How many kanban card sets are needed? (Round up your answer to the next whole number.) Number of kanban card sets