Question

Zn(OH)2 was saturated in a solution of sodium hydroxide. The following equilibra exist under these conditions
Zn(OH)2 -> Zn2+ +2OH- Ksp
Zn2+ +OH- -> Zn(OH)+ K1
Zn(OH)- + OH- -> Zn(OH)2 K2
Zn(OH)2 + OH- -> Zn(OH)3- K3
Zn(OH)3- +OH- -> Zn(OH)42- K4
a) Sum of which species would you use to express the solubility S of zinc hydroxide in the above system
b)Write the expression for the Zn2+ concentration in terms of prevailing OH- concentration
c) Write the expression describing the solubility of zinc hydroxide in solution in term of equilibrium constants and prevailing OH- only

I do not know where to start.