91. Solving a chemistry problem

15. To 50.00 ml of HCl solution (K=0.9500 to 0.2 N) was added 25.00 ml of NaOH solution of unknown concentration. At the same time, the solution medium remained acidic. 2.50 ml of KOH solution (K=1.2780 to 0.1 N) was used for titration of the remaining acid. Determine K(NaOH).