Explanations:

The molar mass of Fe2S3 is 207.9 g/mol. So 34 mol of Fe2S3 weighs 34 mol * 207.9 g/mol = 7068.6 g. Each mole of Fe2S3 contains 2 mol of Fe, so 34 mol of Fe2S3 contains 34 mol * 2 mol Fe / 1 mol Fe2S3 = 68 mol Fe. The molar mass of Fe is 55.85 g/mol, so 68 mol of Fe weighs 68 mol * 55.85 g/mol = 3823.8 g.