114. Solving a chemistry problem

3. V ml of waste water were placed into two volumetric flasks with a capacity of 100.0 ml. 10.00 ml of CuSO4 standard solution (T(Cu) 0.001000) was added to one flask. In both flasks were introduced solutions of ammonia, rubeanic acid and diluted to the mark with water. When photometry solutions received optical densities

V, ml Dx Dx st
20.00 0.280 0.420
Determine the concentration (g/l) of copper in waste water.
Answer: 1.0