139. Solving a chemistry problem

To prepare a reference solution, 0.258 g of lead nitrate was dissolved in 250.0 cm3 of water. After treating 5.0 cm3 of the solution with dithizone, 50.0 cm3 of a colored solution was obtained. The colored compound was extracted with 10.0 cm3 of chloroform, and the optical density of the chloroform layer was found to be 0.35.
A weighed portion of the investigated alloy of 1.0000 g was dissolved in acid and the solution was diluted with water to 100.0 cm3. After treating 10.0 cm3 of this solution with dithizone, 25.0 cm3 of a colored solution was obtained. The colored compound was extracted with 10.0 cm3 of chloroform, and the optical density of the chloroform layer in the same cuvette was found to be 0.14. Determine the lead content in the alloy.