86. Solving a chemistry problem

4. When determining lead in hydrochloric acid, 0.3 ml of the analyzed solution (p = 1.19 g / ml) was frozen with liquid nitrogen, then a luminescence burst Ix = 30 was recorded when the solution was defrosted.
Similarly, a luminescence burst of the analyzed solution with the addition of 0.40 ml of a lead solution containing 0.02 μg Pb / ml (Ix + Δ) = 50 was recorded.
Calculate the mass fraction (%) of lead in the analyzed sample