please help me quickly ????

Calculate the equilibrium solubility of silver arsenate

(Ksp = 6 * 10-23) in a solution that buffered to a pH of :

a) 3

b) 6

c) 9

For H3ASO4

Ka1 = 5 * 10-3

Ka2 = 1.1 * 10-7

Ka3 = 3.2 * 10-12​