To solve this question, we need to use the following formula:
% by mass = (mass of a component/total mass) x 100%
So first, we need to calculate the total mass of the compound:
9.17 + 3.94 = 13.11
Now we can calculate the percent composition of Iron and of Oxygen.
Iron:
% by mass = (mass of Iron/total mass) x 100%
% by mass = (9.17/13.11) x 100%
% by mass = 69.9%
Oxygen:
% by mass = (mass of Oxygen/total mass) x 100%
% by mass = (3.94/13.11) x 100%
% by mass = 30.0%
Answer: 69.9% of Iron and 30.0% of Oxygen