Answer : The mass of water produced will be 32.78 grams.
Explanation : Given,
Mass of  = 21.9 g
 = 21.9 g
Molar mass of  = 72.15 g/mole
 = 72.15 g/mole
Molar mass of  = 18 g/mole
 = 18 g/mole
First we have to calculate the moles of  .
.

Now we have to calculate the moles of  .
.
The balanced chemical reaction will be,

From the balanced reaction we conclude that
As, 1 mole of  react to give 6 moles of
 react to give 6 moles of 
So, 0.3035 moles of  react to give
 react to give  moles of
 moles of 
Now we have to calculate the mass of  .
.


Therefore, the mass of water produced will be 32.78 grams.