In lab, a student weighed out 0.1022 g of succinic acid, dissolved it in 40 mL DI water and added 1 drop of phenolphthalein indicator. She titrated the acid with a NaOH solution whose exact concentration was unknown. A volume of 18.19 mL of NaOH solution was required to reach the endpoint of the titration. What was the concentration of the NaOH solution in units of M (mol/L)?