By titration it is found that 20.5 mL of 0.168 M NaOH(aq) is needed to neutralize 25.0 mL of HCl(aq). Calculate the concentration of the HCl solution

Aren't these the same problem? You didn't look to see your old post?

http://www.jiskha.com/display.cgi?id=1398649923