Wastewater of a town is directly discharged into a reservoir, which has a volume of 50*106 m3. The retention time of the reservoir water is 2 years. The 350 residents of the city, each generate an average of 70 kg/year of contaminant A, all of which is discharged into the reservoir with the town's wastewater. The rate constant for decay of contaminant A in the reservoir is k=1.5 (1/year). Assuming the population, discharge rate, and reservoir conditions have been stable for a long time, estimate the concentration of A in the reservoir.