A student titrated 10.00-mL aliquots of her unknown amino acid solution with standard 0.1521 NaOH and with 0.0986 M HCl. No inflection points were observed with the HCl titrations but two were observed in the titration with NaOH. One occurred after 3.29 mL of titrant had been added and another after a total of 18.61 mL of NaOH had been added. Calculate the concentration of the amino acid.