What Is the Solubility in Moles/L of CaF₂ in Water

What is the solubility in moles/L of CaF₂ in water given that the K_sp is 4.0 x 10 ^{- 11}?

A) 2.2 x 10 ^{- 4}
B) 4.0 x 10 ^{- 11}
C) 3.5 x 10 ^{- 4}
D) 6.0 x 10 ^{- 5}
E) 2.0 x 10 ^{- 11}