3. When carrying out a quantitative analysis of a sample containing cobalt, using the external standard method, four standard samples were used to construct a calibration graph in the coordinates Nov/Next.st – СCo. To obtain reliable data, each standard sample and sample was measured 3 times. Measurement data are shown in the table:
Sample C, % N1(Co) N2(Co) N3(Co)
1 standard 0.90 89450 89540 89855
2 standard 1.40 137920 137760 137462
3 standard 1.70 163490 163196 163243
4 standard 2.40 242380 248560 238670
Sample X 128033 129185 129178
External standard 178854 179064 179709
Determine the concentration of cobalt in the sample.

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