Solve by spreadsheet: A company has been discharging its waste into a holding pond for years. The pond is full and overflowing into a river for the last 6 months. The concentration of the primary waste in the pond is 35 mg/L. All of a sudden, the process changes, and the concentration of the waste in the stream coming into the pond jump to 250 mg/L. The pond is 500,000 L and the flow rate of the waste coming into it is 75,000 L/day. How many hours will it take until the waste concentration in the overflow stream going into the river reaches the danger level of approximately 50 mg/L?