Two concrete mixers of capacity 200 liters each are used in a construction site to produce 20 cubic meter of concrete. Ingredient charging, mixing and discharge times are 3 minutes, 7 minutes and 1 minute respectively. Assuming a time loss of 5 minutes per hour of operation, the total time in hours for the mixers to produce the required amount of concrete will be ___________

• A. 10
• B. 15
• C. 25
• D. 47