How do I balance the equation for iron reacting with steam?

Start with the skeleton equation: Fe + H2O gives Fe3O4 + H2. First balance iron: the product Fe3O4 has 3 iron atoms, so put 3 in front of Fe on the left. Now you have 3 Fe + H2O gives Fe3O4 + H2. Next balance oxygen: Fe3O4 has 4 oxygen atoms, so put 4 in front of H2O. That gives 3 Fe + 4 H2O gives Fe3O4 + H2. Now count hydrogen: the left has 4 times 2 = 8 hydrogen atoms, so put 4 in front of H2 on the right to get 8 hydrogen atoms. The balanced equation is 3 Fe + 4 H2O gives Fe3O4 + 4 H2. Always balance metals first, then oxygen, then hydrogen, and recount each element at the end.