145. Solving a chemistry problem

69. For the determination of magnesium by the calibration curve method, the following data were obtained:
The concentration of the standard solution of magnesium, µg / ml
0.5000 1.0000 1.500
Atomic absorption at 285.2 nm, the number of tick marks
19.5 36.0 55.0
A weighed alloy weighing 0.1000 g dissolved in a mixture of acids and transferred to a volumetric flask with a capacity of 200.00 ml. Before analysis, the solution was diluted 20 times. In this case, the atomic absorption turned out to be equal to 30.0 divisions of the scale.
Determine the mass fraction (%) of magnesium in the alloy.