Needing help for chemistry

Question

How many grams of oxygen are combined with 14.6 grams of iron to make the iron(II) oxide compound?

Answer 1

Iron(II) oxide = FeO

atomic mass Fe = 55.85 g/mol

atomic mass O = 15.999

molar mass FeO = 72.85 g/mol

14.6 g FeO x 1 mol FeO / 72.85 g x 1 mol O / mol FeO x 15.99 g O/mol O = 3.21 g O

Done another way, using % composition:

% by mass of O in FeO = 15.999 g / 72.85 g = 0.2196 = 21.96% by mass

21.96% x 14.6 g = 3.21 g O