50. Solving a chemistry problem

4. Moss P. schreberi weighing 5.3245 g was mineralized in nitric acid and placed in a 50.00 cm3 flask, two samples of 20.00 cm3 each were placed in flasks with a capacity of 50.00 cm3. A solution containing 0.50 mg of iron was added to one flask. Both flasks were added with 1 cm3 of HNO3 (1:1), 5 cm3 of 10% sulfosalicylic acid and made up to the mark with water. Calculate the iron content in moss in µg/g of dry matter, if the following data were obtained during photometry of solutions at  = 510 nm in a cell with a layer thickness of 2 cm: Ax = 0.28, and Ax+st = 0.50.