Time to drain a reservoir with flow 4.5 L/min and volume 900 mL?

• A. 6 seconds
• B. 12 seconds
• C. 24 seconds
• D. 60 seconds

Answer: (B)

Time to drain is found by dividing the volume by the flow rate. Convert 900 mL to liters: 0.9 L. The flow is 4.5 L per minute, so time in minutes is 0.9 / 4.5 = 0.2 minutes. Convert to seconds: 0.2 × 60 = 12 seconds. So the drain time is 12 seconds. The other options would require different volumes or flow rates (e.g., 0.1 min is 6 s, 0.4 min is 24 s, 1 min is 60 s), which don’t match the given values.