9. Solving a chemistry problem

3. To determine the content of lead in zinc ore by the addition method, a sample of ore 3.1860 g was dissolved and, after appropriate treatment, the volume of the solution was brought to 500.0 ml. When removing the polarogram, 50.0 ml of this solution was taken. The wave height turned out to be 25.0 mm. After adding 5.0 ml of 0.08 M Pb(NO3)2, the wave height increased to 27.0 mm. Determine the percentage of lead in the ore.