Calculate x in the formula FeSO₄· x H₂O from the following data: 12.18 g of iron(II) sulfate crystals were made up to 500 cm³ acidified with sulfuric acid in a volumetric flask. 25.0 cm³ of this solution required 43.85 cm³ of 0.0100 mol dm⁻³ KMnO₄ for complete oxidation.