Equation: Fe2O3 + 3C => 2Fe + 3CO
Don't forget to balance your equation.
We need the mass of C to react with 125 g of Iron oxide, Fe2O3.
For this, we must have the atomic mass of C and the molar mass of Fe2O3:
For C) 12.0 g/mol
For Fe2O3) 159 g/mol
Procedure: use stoichiometry
3 x 12.0 g C --------- 159 g Fe2O3
x --------- 125 g Fe2O3
x = 28.3 g
Answer: Mass of C needed = 28.3 g