Think about the overall equation and look at the molar ratio (1 to 1 to 1). Work out the number of moles of both Fe and S you'll find that sulphur is in excess so iron is the limiting reactant and reacts completely whereas some sulphur will remain at the end of the reaction - so the maximum number of moles of FeS that you could possibly form from this is equal to the number of moles of iron. You multiply this by the molar mass of FeS and get 4.4g.