What Is the Concentration of F ^- Ions in a Solution

What is the concentration of F ^- ions in a solution prepared by saturating a 0.0045 M Ba(NO₃) ₂ solution with BaF₂?
( K _sp = 1.0×10 ^{- 6})

A) 2.2×10 ^{- 4} M
B) 1.0×10 ^{- 6} M
C) 4.5×10³ M
D) 1.5×10 ^{- 2} M
E) 4.5×10 ^{- 2} M