The answer is (1) 0.125 M. The reaction equation is NaOH + HCl = NaCl + H2O. So the mol number of NaOH and HCl is the same. So suppose the concentration of HCl is x, we can have equation: 20*1.15=24*x. So x= 0.125 M. (M means mol/L, but if we use the same unit at both side of the equation, it is ok.)