The dissociation equation is:
AgNO3 = Ag+ + NO3-
We write the Ksp expression.
Ksp = [Ag+] [NO3-]
Since there is 1:1 molar ratio, we can assign the two values at the right side with s which represents the molar solubility.
1.8E^-10 = (s)(s)
1.8E^-10 = s^2
s=1.34 x 10^-5 M