As the given equation is
AgNO3 = Ag+ + NO3-
split it then derive the
the Ksp expression.
Ksp = [Ag+] [NO3-]
Since there is 1:1 molar ratio,so by applying values
1.8E^-10 = (s)(s)
1.8E^-10 = s^2
s=1.34 x 10^-5 M
this is the solubility of silver chloride
hope it helps