What Is the Concentration of Hg₂²⁺ in a Saturated Solution

What is the concentration of Hg₂²⁺ in a saturated solution of Hg₂Cl₂ if K_sp = 1 × 10−¹⁸?

A) 1 × 10−⁹ M
B) 2 × 10−⁹ M
C) 3 × 10−⁷ M
D) 6 × 10−⁷ M
E) 1 × 10−⁶ M