For an equation to be balanced, the number of atoms of the reactants and products have to be equal. Therefore, (3) 3Fe3++ Al → 3Fe2++ Al3+ is the balanced equation, as you have 3 Fe atoms and 1 Al atom on both sides. The exponents are just the charges of the elements, and you don't need to care about these numbers in order to balance a chemical equation.
Hope this would help :))
