2.25 units.
Explanation:
Processing time is 5 minutes per unit for step 1. The total capacity is 60 minutes then no. of units produced can be;
60 / 5 = 12 units per hour.
For second step processing time is 4 minutes per unit. There is 0.85 unit of product is scrapped. Then no. of units produced per hour can be ;
60 / 4 = 15 units per hour.
After scrap the net product units per hour will be;
15 units * [1 - 0.85] = 2.25 units per hour.