106. Solving a chemistry problem

To build a calibration graph in the determination of nickel, 2.5 was selected; 5.0; 7.5; 10.0; 12.5; 15.0 ml of 0.0125 N NiCl2 solution and diluted with water to 100.0 ml. The deviation on the scale of the galvanometer on a single-beam photoelectrocolorimeter for the zero solution was 80 divisions, and for the indicated solutions 72.5; 64.5; 59.0; 62.5; 47.0; 42.5 divisions, respectively. A sample of steel 0.5000 g was dissolved and then diluted with water to 50.0 ml. The deviation on the galvanometer scale for the resulting colored solution under the same conditions was 55.5 divisions. Determine the nickel content in steel (in%).