I'm not too sure about what you mean by over-substituting,
well, i do know what you mean, but are my equations over-substituted?
i mean, there are two variables and i have two equations
I know that those equations can be used to solve the question,
I've been told that they will work...
I took a look at the equation you suggested,
it tells me that [S2-]=2[Ag+],
which is equal to the solubility of silver sulfide