A technician assembles lens. Starting from parts, the technician can assemble a lens at the rate of 4 per hour. 90% of the newly assembled lens pass a calibration test and are then considered completed units. However, the newly assembled lens that fail the calibration test must be recalibrated by the technician. The technician requires 10 minutes to recalibrate a lens. 100% of recalibrated lens pass the subsequent calibration test and are then considered completed units. The technician prioritizes recalibration work, meaning that if there are lens to recalibrate then the technician works on them before starting new lens. How many completed lens does the technician produce per hour (units/hr)