The formula is %age by mas of water of crystallization = [(Number of molecules of water x  Molar mass of water) / Molar mass of hydrated salt] x100

 i.e % by mass of water of crystallization = \(\frac{18x}{molar mass of MSO4.XH\(_2\)O} \times 100\)

Number of molecules of H\(_2\)O X Molar mass of H\(_2\)O = 18X

Molar mass of hydrated salt, MSO4.XH\(_2\)O = 56 + 32 + (16 X 4) + 18X = 152 + 18X

% by mass of H\(_2\)O of crystallization = 45.3%

% by mass of H\(_2\)O of crystallization = \(\frac{18x}{152 + 18x}\times 100\)

  45.3% = \(\frac{18x}{152 + 18x}\times 100\)

 \(\frac{45.3}{100}\) = \(\frac{18x}{152 + 18x}\)

 100 x 18X = 45.3(152+18X)

  1800X = 6885.6 + 815.4X

 1800X - 815.4X = 6885.6

  984.6X = 6885.6

 X = \(\frac{6885.6}{984.6}\)

 X = 6.993

 X = 7.