145. Solving a chemistry problem

67. When determining tin in bronze by the method of comparison, a portion of bronze weighing 0.2500 g was dissolved in a mixture of acids and transferred to a volumetric flask with a capacity of 100.00 ml. Atomic absorption at 286.3 nm of this solution and the standard with a concentration of 1.0000 mg of Sn in 1.00 ml was found to be 6.5 and 9.0 units of the scale, respectively. Determine the mass fraction of tin in bronze.