What concentration of SO2−3 is in equilibrium with Ag2SO3(s) and 7.90×10−3 M Ag+ ?

Answer 1

I'll assume you have a typo in the question and meant to ask about SO₃^2- and not SO₂^3-

Ag₂SO₃(s) <==> 2Ag⁺(aq) + SO₃^2-(aq)

At equilibrium, the [SO₃^2-] will be 1/2 the [Ag⁺] as shown in the equilibrium equation above.

[SO₃^2-] = 7.90x10^-3 / 2 = 3.95x10^-3 M = [SO₃^2-]