In order to balance the equation, Mg3N2+xH2O→3Mg(OH)2+2NH3, the value of x is
6
Check the number of atoms on both L.H.S and R.H.S. In the balanced equation, the number of atoms on both sides should be equal.
Therefore the equation is : Mg3N2+6H2O→3Mg(OH)2+2NH3.