A supplier of instrument gauge clusters uses a kanban system to control material flow. The gauge cluster housings are transported eight at a time. A fabrication center produces approximately 15 gauges per hour. It takes approximately four hours for the housing to be replenished. Due to variations in processing times, management has decided to keep 20 percent of the needed inventory as safety stock. How many kanban card sets are needed? (Round up your answer to the nearest whole number.)