Chemistry - manganate titrations

I have no idea how to do this question... so any help would be highly appreciated!

Ethanedioic acid, H₂C₂O₄, is a reducing agent. On reaction with manganate the H₂C₂O₄ is oxidised to CO₂ and the MnO₄^- reduced to Mn²⁺. A sample of hydrated ethanedioic acid, H₂C₂O₄^.xH₂O, weighing 0.980g was dissolved in water and the solution made up to 250cm³. 25cm³ samples of the solution were transferred to a conical flask and titrated with 0.01moldm^-3 potassium manganate (VII). The ethanedioic acid in the solution required 31.1cm³ of the potassium manganate (VII) solution for reaction. Calculate the value of x, the number of waters of crystallisation.

Thanks in advance.