AgCl \leftrightarrow Ag+ + Cl -
let at time of equlibrium [Ag]= y M
and [Cl]= x = slubility of AgCl
xy= Ksp .................. (1)
now
Ag+ + 2 NH3 \leftrightarrow Ag(NH3)2+ K=1/Kc
now [Ag(NH3)2+ ] = x-y M
=> x-y/y= K=1/Kc
neglecting change in conc. of NH3.
=> x/y= 1/Kc ............ (2)
solving one and two x = \sqrt{\frac{K_{sp}}{K_{c}}}