135. Solving a chemistry problem

8. To construct a calibration graph in the determination of vanadium, standard samples of steel СО were taken, containing the following amounts of vanadium: 1 - 0.15; II - 0.33; III - 0.58; IV - 0.72%. Samples of steel CO, 0.5 g each, were dissolved, and after treatment with hydrogen peroxide, 50 ml of colored solutions were obtained. When photometry of these solutions (I-IV) on a single-beam photocolorimeter, the following deviations were obtained on the galvanometer scale: background-100; I - 79; II - 61; III - 41.5; IV -34.5.
Determine the content of vanadium in the test sample (in%), if for it under the same conditions the deviation on the galvanometer scale was 52.5 divisions.