81. Solving a chemistry problem

9. Acetic acid solution with a volume of 1000 ml contains 0.0521 g of the dissolved preparation of riboflavin (vitamin B2). An aliquot of this solution (20 ml) was diluted with aqueous sodium acetate to 100 ml. The optical density of the obtained solution turned out to be 0.837 at 267 nm and l = 2 cm. Calculate the content (%) of B2 (C17H20N4O6) in the analyzed solution if ε (riboflavin)267 = 32000 l/(mol*cm).