First, find the molar mass of Fe2O3. Looking at the periodic table and doing the appropriate calculation we see that Fe2O3 has a molar mass of 159.687 g/mol.
We need to completely react 125g of Fe2O3--convert the mass of Fe2O3 to mols...
125 g Fe2O3 x (1 mol Fe2O3) / (159.687 g Fe2O3) = 0.782781 mols Fe2O3
Now the question asks "How many grams of carbon are needed to completely react with 125g of Fe2O3?"
Looking at the balanced eqn above I don't see any carbon so I'm not certain I have all of the info I need to completely answer the question. I'll do two calculations based upon what I think might be meaningful.
1) I wonder if instead we are asked to find the grams of AlCl3 needed to completely react with the 125g Fe2O3.
In that case we use the molar mass of AlCl3 (133.341 g/mol) to find the mass of AlCl3 needed.
0.782781 mol Fe2O3 x (2 mol AlCl3) / (1 mol Fe2O3) x (133.341 g AlCl3) / (1 mol AlCl3) = 208.753 grams
= 208 g AlCl3 (with sigfigs)
2) Alternatively (and this is a shot out of the dark) suppose that we are asked to find the amount of carbon needed to reduce iron oxide to elemental iron...