23. Solving a chemistry problem

1. Calculate the % nickel content in steel, a sample of which m = 0.100 g was dissolved, and the volume of the solution was brought to 100 ml. For analysis, 5.0 ml of sample was taken, placed in a 100 ml volumetric flask, and reagents and water were added to the mark. We applied the differential method with the construction of a calibration graph. The concentration of the standard solution is 0.10 mg/ml.
V standard solution, ml 1.0 3.0 4.0 5.0 7.0
Optical density A -0.25 -0.08 0.00 0.10 0.28
The optical density of the test solution is 0.20.