011. Solving a chemistry problem

2. When determining Mn in steel, a 0.200 g sample was dissolved, Mn was oxidized to MnO4- and the solution was diluted to 0.200 ml. Photometry was carried out by a differential comparison method with a standard solution Cst = 20 mg/l and a zero solution with a KMnO4 concentration of 0.0005 N. The optical densities of the test solution and the standard solution relative to the zero solution were respectively: Ast′= 0.28; Ax′= 0.15. Find the % Mn content in steel.