[Equilibrium] Max of A in Saturated Solution B

[brbrett]

Homework Statement

What is the maximum [CO₃^2-] that can exist in a saturated solution of AgBr?

Homework Equations

Equilibrium Constants, ICE tables
sqrt = square root

The Attempt at a Solution

Ksp = [Ag+][Br-]
sqrt(5.4E-13) = x (Ag and Br are in equal proportion to one another)
where x = [concentration] of Ag+

Ksp = [Ag+]²[CO₃^2-]
8.5E-12 = (2(sqrt(5.4E-13)))² [CO₃^2-]
[CO₃^2-] = 3.95

However, the key has an answer of 16 M. Multiplying my current answer by 4 gives something close, but regardless, I'm missing something in my calculations. Thanks for any help~

 

[Borek]

8.5E-12 = (2(sqrt(5.4E-13)))² [CO₃^2-]

Why 2?

16M looks wrong to me, as if it was missing a comma.