Initially, a 200.0 L vessel contained 2.864 mol of SO2, 3.352 mol of O2 and 1.556 mol of SO3. The following reaction was allowed to come to equilibrium

2SO2(g) + O2(g) ⇌ 2SO3(g)

and the equilibrium mixture was found to contain 2.672 mol of O2. Find the value of Kc for this reaction.