The concentration of ammonium ion in the solution of the salt called ferrous ammonium sulfate, formula [Fe(NH4)]2(SO4)3, is 0.360 M. The concentration of sulfate ions in this solution is?

Answer 1

But that isn't ferrous ammonium sulfate. The correct formula is Fe(NH4)2(SO4)2.
IN YOUR COMPOUND, (NH4)^+ is 0.360 so (SO4)^2- = 0.360 x (3 mols SO4/2 mols NH4) = 0.360 x 3/2 = ?