10. In the photocolorimetric determination of Fe3 with sulfosalicylic acid from a standard solution containing 10 mg/cm3 of iron, a series of dilutions were prepared in 100 cm3 volumetric flasks, the optical absorption was measured and the following data were obtained:
Vst, cm3 1.0 2.0 3.0 4.0 5.0 6.0
A 0.12 0.25 0.37 0.50 0.62 0.75
Determine the concentration of Fe3 in the analyzed solutions if their optical absorption is 0.31 and 0.55.

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