Helping those who are in need of help with various Chemistry related topics...
We know that the transition metal has a charge of positive 3, and we should have already known, from past knowledge, that Oxide, or Oxygen, has a charge of negative 2. Fe+3 and O-2. Now we must take the numbers for a walk. Fe+3 O-2 becomes Fe2O3.
Example: Tin (IV) Iodide
Remember that we do not include the 1, because it is understood to be there, even if we do not write it.
Note: the first element is always a positive!