<p>13.4 g of a sample of unstable hydrated salt :&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>N</mi><msub><mi>a</mi><mn>2</mn></msub><mi>S</mi><msub><mi>O</mi><mn>4</mn></msub><mo>.</mo><mi>n</mi><msub><mi>H</mi><mn>2</mn></msub><mi>O</mi></math>&nbsp;was found to contain 6.3 g of water. Determine the number of water of crystallisation.</p>