141. Solving a chemistry problem

From a weighed sample of chemically pure lead acetate weighing 0.3260 g, 100 ml of a solution was prepared. In volumetric flasks of 50 ml were placed: 2,4,6,8,10 ml of the resulting solution, added a stabilizing colloid and diluted sulfuric acid to form a precipitate of lead sulfate. Brought these solutions in volumetric flasks to the mark and measured the optical density.
V, ml 2 4 6 8 10
Optical density 0.22 0.27 0.32 0.4 0.65
A 50 ml sample of running water was diluted to 200 ml and 10 ml of the resulting solution was treated with the same reagents as the standard solutions. The optical density of the test sample was 0.53. Determine the concentration of lead in water in (g / l).