2. Solving a chemistry problem

15. From a sample of steel 0.2162 g, after appropriate processing, 1000 ml of a colored solution of oxidized nickel dimethylglyoximine were obtained. The relative optical density of this solution, measured with respect to a reference solution containing 30 mg/l nickel, was found to be 0.66. Optical density of four standard solutions containing 9.0; 15.0; 18.0 and 24.0 mg of nickel in 1000 ml, found to be equal to 0.22, respectively; 0.48; 0.60; 0.87. Build a calibration graph in the coordinates A-C (mg/ml) and determine the percentage of nickel in the steel.