Chem AS level question

2.5 grams of solid hydrated ethanedioic acid was made up to a 250 cm3 solution using a distilled water in a volumetric flask. Of this solution, 15.8 cm3 was required to neutralise 25cm3 of 0.1 moldm^3 NaOH in a titration. Work out the number of moles of water per mole of acid in the original solid sample.
Thanks in advance!

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