A level Chemistry Question?

5.13 grams of washing soda crystals (hydrated sodium carbonate) were dissolved in deionised water and made up to 250 cm^3 of solution in a volumetric flask. A 25.0 cm^3 aliquot of the solution require 25.90 of 0.0690 mol/dm^3 sulfuric acid solution for neutralization. Calculate the percentage of anhydrous sodium carbonate in the sample.