What Will Be the Equilibrium Concentration of Silver(I)ion in an Aqueous

What will be the equilibrium concentration of silver(I) ion in an aqueous solution originally containing 0.00100 M Ag⁺ and 0.500 M 1,10-phenanthroline?
Ag⁺(aq) + 2 phen(aq) $\leftrightarrows$ [Ag(phen) ₂]⁺(aq) K_f = 1.2 $\times$ 10¹² [Ag (phen) ₂]⁺

A) 9 $\times$ 10^-7 M
B) 8 $\times$ 10^-13 M
C) 6 $\times$ 10^-6 M
D) 3.4 $\times$ 10^-15 M
E) 1.2 $\times$ 10^-12 M