Question: how to find the moles of water formed?
Answer: If 1 mole of HCl or NaOH gives you 1 mole of H2O , then the number of moles in H2O is: [ 1÷1×1 ] = 1 mole.
Now you have to find out the molar mass (M) of water ( H2O ). ... 
Therefore the molar mass (M) of H2O is: ... 
Last step, find the mass (m) of water.