The ksp of aluminum hydroxide is 5.6e-17. What is the concentration of hydroxide in a saturated solution?

...........Al(OH)3 ==> Al^3+ + 3OH^-

.......for x moles......x.......3x

Ksp = (Al^3+)(OH^-)^3
Plug in Ksp, (Al^3+) = x and (OH^-) = 3x