121. Solving a chemistry problem

5. 10.00 ml of hydrogen peroxide solution was diluted with water to 200.0 ml in a volumetric flask. To 20.00 ml of the resulting solution was added an excess of potassium iodide and acidified with sulfuric acid. 15.65 ml of a 0.1M solution of sodium thiosulfate (K = 0.9800) was used to titrate the released iodine. Determine the mass of hydrogen peroxide in the initial solution.