17. Solving a chemistry problem

183. 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 according to the following data:
Task number 183
V, ml 0.2
Iх, scale divisions 20
Iх+Δ, scale divisions 40