Explain the equilibrium constant of the reaction

Question

At 750degrees Celsius the following reaction was performed in a sealed vessel:
H₂(g) + I₂(g) .<=> 2HI (g)

Explain the equilibrium constant of the reaction at this temperature when the starting concentration of H₂ is 3.9 M, and the starting concentration of I₂ is 3.00 M, and the equilibrium concentration of I₂is6.00*10^-2 .