A solution contains $1\mathrm{.}49{10}^{-2}M$ iron$($III$)$ nitrate and $1\mathrm{.}26{10}^{-2}M$ zinc acetate.

Solid ammonium sulfide is added slowly to this mixture.

What is the concentration of iron$($III$)$ ion when zinc ion begins to precipitate?

$[F{e}^{3+}]=,M$