Amixture initially contains a, b, and c in the following concentrations: [a] = 0.350 m , [b] = 0.900 m , and [c] = 0.350 m . the following reaction occurs and equilibrium is established: a+2b⇌c at equilibrium, [a] = 0.150 m and [c] = 0.550 m . calculate the value of the equilibrium constant, kc. express your answer numerically.