140. Solving a chemistry problem

IV. After appropriate processing of four standard steel samples containing chromium, their polarograms were taken and the following results were obtained - table 20.
Table 20

Samples 1 2 3 4
CCr,% 0.30 0.42 0.96 1.40
h, mm 8.0 10.0 20.0 28.0

Build a calibration graph and determine the percentage of chromium in the analyzed sample for the following task numbers - Table 21.
Table 21

Problem number hX, mm
71 22.0