90. Solving a chemistry problem

6. For the luminescent determination of riboflavin (vitamin B2) in a food product by the addition method, 0.1500 g of the product was dissolved and, after appropriate treatment, the luminescence intensity of the resulting solution was measured. It turned out to be 25. After adding a standard solution containing 26 µg of vitamin B2, the luminescence intensity increased to 60. Determine the mass fraction of vitamin B2 in the product if the luminescence intensity of the blank solution is 12.