To determine the mass of the iron powder, you need to subtract the mass of the weighing dish from the total mass of the dish with the iron powder.
Given that the mass of the weighing dish is 2.1 grams and the total mass of the dish with the iron powder is reported as 134.313 grams, you can calculate the mass of the iron powder as follows:
Mass of iron powder = Total mass - Mass of weighing dish
= 134.313 grams - 2.1 grams
= 132.213 grams
Therefore, you should report the mass of the iron powder as 132.213 grams.