145. Solving a chemistry problem

58. When determining manganese in the alloy by the method of additives, a weighed mass of 0.5000 g was dissolved and the solution was diluted to 200.00 ml. Four identical portions of the solution were taken and equal volumes of standard manganese solutions containing 0, 2, 4, 6 μg / ml Mn were added to each portion. The atomic adsorption spectrophotometer measured the optical density for an analytical line of 279.48 nm by spraying the solutions in acetylene-air flame. Received respectively 0,225 0,340 0,455 0,570. Calculate the mass fraction of manganese in the alloy.