The student decides to determine the molarity of the same Na2CO₃ solution using a second method. When Na2CO3 is dissolved in water, CO₃²−(aq) hydrolyzes to form HCO₃⁻(aq), as shown by the following equation. CO₃²⁻(aq) + H₂O(l)  HCO₃ −(aq) + OH−(aq) Kb = [HCO3⁻][OH⁻]/ [CO3²⁻ ] - - - = 2.1 × 10⁻⁴. Explain how the student could use the measured value in part (f)(i) to calculate the initial concentration of CO₃²⁻(aq). (Do not do any numerical calculations.)