30. Solving a chemistry problem

182. To determine riboflavin (vitamin B2) by the additive method, a sample of a food product weighing 0.2005 g was dissolved and, after appropriate treatment, the luminescence intensity of the resulting solution was measured, obtaining Ix = 35. After adding a standard solution containing 40 μg of vitamin B2, the luminescence intensity increased to Iх Δ = 80. Determine the mass fraction of vitamin B2 in the product if the luminescence intensity of the blank solution is 10.