24. Solving a chemistry problem

102(3). To construct a calibration graph for nephelometric determination of sulfate ion 25.0 ml. H2SO4 solution with a concentration of 0.263 mg/ml was diluted to 100 ml. Then, BaSO4 suspensions were prepared in 100 ml volumetric flasks containing V ml of this solution, their apparent optical densities were measured and the following was obtained:
V ml 25.0 15.0 10.0 6.0 2.0
A (each) 0.21 0.32 0.50 0.68 1.02

Sample V1 of the analyzed solution was diluted to 100 ml, then 100 ml of BaSO4 suspension was prepared from 20 ml of this solution.

Determine the content of SO3, mg/l in the analyzed solution, if the apparent optical density is: V1 - 10.0 A(each) - 0.46