At what rate is water discharged on 7 am if the flow reads 6.4 mgd?

The correct answer is based on the interpretation of the flow reading. If the flow meter reads 6.4 million gallons per day (mgd) at 7 am, this value indicates the current discharge rate at that specific time. The reading of 6.4 mgd means that the facility is discharging that quantity of water, and no additional context or calculations are necessary to determine the rate since it is directly provided by the flow meter.

This reading reflects either the operational capacity of the system at that moment or the total volume being processed or released. The other options present different values, which do not match the indicated reading, making them irrelevant to the question asking for the current discharge rate.