A pond with a volume of 4000m3 has been receiving water at a flow rate of 20m3/d from a stream and 10m3/d from a factory. The water in the stream has a concentration of compound A of 10mg/L, while the water from the factory has a concentration of 100mg/L. Compound A degrades at a rate of 2.0103 per day in the pond. Water begins to be diverted from the stream for agricultural use, dropping the flow entering the pond from the stream to 10m3/d. What is the concentration (in mg/L ) of compound A in the pond 30 days after the water begins to be diverted