How many grams of C are required to react with 11.8g of Fe2O3?

Molar mass of C = 12.0 g/mol
Molar mass of Fe₂O₃ = (55.8×2 + 16.0×3) g/mol = 159.6 g/mol

3C + 2Fe₂O₃ → 4Fe + 3CO₂
Mole ratio C : Fe₂O₃ = 3 : 2

Moles of Fe₂O₃ reacted = (11.8 g) / (159.6 g/mol) = 0.0739 mol
Moles of C required = (0.0739 mol) × (3/2) = 0.111 mol
Mass of C required = (0.111 mol) × (12.0 g/mol) = 1.33 g

OR:
(11.8 g Fe₂O₃) × (1 mol Fe₂O₃ / 159.6 g Fe₂O₃) × (3 mol C / 2 mol Fe₂O₃) × (12.0 g C / 1 mol C)
= 13.3 g