At a certain temperature, 0.820 mol SO₃0.820 mol SO₃ is placed in a 3.50 L3.50 L container.

2SO₃(g)↽−−⇀2SO₂(g)+O₂(g)₂SO₃(g)↽−−⇀2SO₂(g)+O₂(g)

At equilibrium, 0.130 mol O₂0.130 mol O₂ is present. Calculate Kc.