-When Ksp is the solubility product constant for a solid substance when it 
dissolved in an aqueous solution, and measure the level at which a solute 
dissolves in the solution.
- and we have the solubility and it is the maximum quantity of solute which can dissolve in a certain solute 
we can assume the solubility = X = 2.2 x 10^-5 M
and when the balanced reaction equation is:
Mn(OH)2(s)  ↔ Mn2+   +  2OH-
∴ the Ksp expression is = [Mn2+] [OH-]^2
when [Mn2+] = X = 2.2 x 10^-5 M
and [OH-] = 2X = 2*(2.2 x 10^-5) = 4.4 x 10^-5 M
by substitution:
∴ Ksp = X * (2X)^2
           = (2.2 x 10^-5)(4.4 x 10^-5)^2
           = 4.3 x 10^-14