Solubility combined with Buffer solutions ugh

[ultimateguy]

Homework Statement

Calculate the solubility of C6H5COOAg(s) in a buffer solution that has a pH of 3.20. (Ka = 6,5 x10^-5M ; Ksp = 2,5 x10^-5M^2)
a) 0,0164M
b) 0,0050M
c) 0,0287M
d) 0,0012M

Homework Equations

Henderson-Hasselbach, Ksp equation

The Attempt at a Solution

This is driving me nuts. I used Henderson-Hasselbach to find [C6H5COO], wrong answer, tried an equilibrium problem, wrong answer. Can someone give me a method for this. Thanks.

 

[xiankai]

could you illustrate your workings, maybe there is a calculation error or a way you used your equations wrongly

 

[Borek]

What is your buffer concentration? Knowing pH you can only calculate acid/base ratio, not their real concentrations.