Equilibrium constant

Equal quantities of hydrogen and gaseous iodine at 700 K (427oC) are placed in a reaction vessel and allowed to reach equilibrium according to the following equation:
H2 (g) + I2 (g) 2 HI (g)
If the following equilibrium concentrations are measured: [H2] = [I2] = 0.021 mol/L and [HI] = 0.158 mol/L, what is the equilibrium constant for this reaction at 700 K?
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