In the study of the conversion of methane to other fuels, a chemical engineer mixes gaseous methane and water in a 0.32 L flask at 1200 K. At equilibrium the flask contains 0.26 mol of CO, 0.091 mol of H₂ and 0.041 mol of CH₄. What is the [H₂O] at equilibrium? K_c = 0.26 for this process at 1200 K.