3. Solving a chemistry problem

2. In the photometric determination of the iron content in wastewater, the standard method was used, for which 25.0 cm3 of samples and a standard solution of iron with a concentration of 25 μg/ml were used. The optical densities of these solutions at 248.32 nm are 0.350 and 0.640, respectively. Determine the concentration of iron in wastewater (mg/dm3).