At elevated temperatures, hydrogen iodide may decompose to form hydrogen gas and iodine gas, as follows:

2HI(g) ⇌ H2 (g) + I2 (g)

In a particular experiment, the concentrations at equilibrium were measured to be [HI] = 0.85 mol/L, [I2] = 0.60 mol/L, and [H2] = 0.27 mol/L. What is Kc for the above reaction?