145. Solving a chemistry problem

145. Solving a chemistry problem

76. In the determination of iron in wastewater, the method of standard additives was used. For this purpose, 20.00 ml of waste water was poured into two volumetric flasks with a capacity of 25.00 ml, and 2.00 ml of a standard solution of iron with a concentration of 0.50 μg / ml was poured into one of them. The volumes of solutions in both volumetric flasks brought to the mark with distilled water. The atomic absorption of these solutions at 248.32 nm is 25 and 15 units, respectively.
Determine the concentration (mg / l) of iron in the waste water.