84. Solving a chemistry problem

156. A sample weighing 0.4566 g containing potassium bromide and indifferent impurities was dissolved in a 100.0 ml volumetric flask. To 15.00 ml of the resulting solution, 20.00 ml of silver nitrate solution was added, C(AgNO3) = 0.05036 mol/l. The unreacted silver ions were titrated with 10.98 ml of ammonium thiocyanate solution with a concentration of 0.05046 mol/l. Calculate the mass fraction of potassium bromide in the sample.