Hey there!
Fe + O₂ → Fe₂O
Let's start by balancing the oxygen.
There are two on the left and one on the right, so let's add a coefficient of 2 in front of Fe₂O.
Fe + O₂ → 2Fe₂O
Now let's balance the iron.
There is one on the left and four on the right, so let's add a coefficient of 4 in front of Fe.
4Fe + O₂ → 2Fe₂O
This is our final balanced equation.
Hope this helps!