66. Solving a chemistry problem

2. To determine vitamin PP in canned fish "Pink salmon", a sample of 20.0000 g was taken and after its decomposition, 50 cm3 of solution was obtained. The luminescence intensity measured with a fluorimeter was 0.72. For a standard solution containing 0.26 mg of vitamin PP in 50 cm3, the luminescence intensity was 0.36. Calculate the mass fraction of vitamin PP in the sample.