From the periodic table:
mass of iron = 55.8 grams
mass of oxygen = 16 grams
molar mass of Fe2O3 = 2(55.8) + 3(16) = 159.6 grams
mass of iron in Fe2O3 = 2(55.8) = 111.6 grams
Mass percent of iron can be calculated by dividing the mass of iron by the mass of the compound and then multiplying the quotient by 100 to get the percentage.
Based on this:
mass % of iron = (111.6/159.6)*100 = 69.92%
