142. Solving a chemistry problem

Upon condensation with aniline, furfural C4H3OCHO forms a red compound C4H3OCH (C6H4NH2) 2, whose molar absorption coefficient at 518 nm is ε1 518 = 6.20 · 104. Furfural and its derivatives form compounds upon condensation with benzidine
yellow color. At 413 nm, the molar absorption coefficients of the condensation products are: ε1 413 = 2.00 · 102 (for furfural), ε2413 = 1.00 · 103 (for methylfurfural and other derivatives). V (ml) of plastic wastewater was taken for analysis; furfural and its derivatives in a flask with a capacity of 500.0 ml and brought to the mark with water. To a 5.00 ml aliquot was added the prepared reagent mixture containing
aniline, and diluted with water to 20.00 ml. The optical density was measured at 518 nm (A518) in a cuvette l = 1.0 cm. To another 50.0 ml aliquot, a hydrochloride solution of benzidine was added and diluted to 100.0 ml. The optical density was measured at 413 nm (A413) in a cuvette l = 5.0 cm.
Calculate the concentration (mg / l) of furfural (M (C4H3OCHO) = 96.0854 g / mol) and its derivatives based on methyl furfural [M (C5H5OCHO) = 110.1158 g / mol] in wastewater for the following data: