0722. Solving a chemistry problem

185. To determine lead in hydrochloric acid, V (ml) of the analyzed solution (ρ = 1.19 g/ml) was frozen with liquid nitrogen, then a burst of luminescence Ix was recorded when the solution was defrosted. Similarly, a burst of luminescence was recorded from a solution with the addition of 0.40 ml of a lead solution containing 0.02 μg Pb/ml (Ix + Δ). Determine the mass fraction (%) of lead in the analyzed sample using the following data:
Problem number 185
V, ml 0.3
Iх, scale divisions 30
Iх+Δ, scale divisions 50