What Is the Minimum Concentration of Br ^- Ions

What is the minimum concentration of Br ^- ions necessary to precipitate PbBr₂ from a 0.080 M Pb(NO₃) ₂ solution, if K _sp = 4.0×10 ^{- 5} for PbBr₂?

A) 5.0×10 ^{- 4} M
B) 0.022 M
C) 6.3×10 ^{- 3} M
D) 1.0×10 ^{- 5} M
E) 0.080 M