Calculate the concentration of calcium (in mg/L) by an appropriate technique. Na⁺ 145 mg/L K⁺ 15 mg/L Mg²⁺ 22 mg/L Ca²⁺ ??? SO4^2- 1115 mg/L Cl^- 15 mg/L HCO₃^- 150 mg/L SiO₂⁰(aq) 21 mg/L