7. To build a calibration graph when determining zinc, equal amounts of a 0.045 mol/l solution of zinc chloride were taken into volumetric flasks with a capacity of 50 ml, processed, brought to the mark with water, and then polarographed. The following results were obtained:
V(ZnCl2), ml 2 4 6 8 12 16 20 24
h, mm 7 13 18 25 36 45 56 68
Build a calibration graph and determine what zinc content (in g) corresponds to a wave height of 31; 17; 51 mm.

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