54. Solving a chemistry problem

3,000 g bronze was dissolved in sulfuric acid and the solution was transferred to a 200 ml volumetric flask. 31.25 ml of Na2S2O3 solution with TNa2S2O3 = 0.0079 g/ml was used to titrate 20 ml of this solution by the iodometric method. To determine the tin content, 20.0 ml of this solution was titrated by a potentiometric method of a potassium bichromate solution with TK2Cr2O7 = 0.0049 g/ml. Its consumption was 16.86 ml. Find the content of Cu and Sn in the sample.