A400.0 ml sample of 0.10 mba(oh)2 is titrated with 0.10 mhbr. determine the ph of the solution before the addition of any hbr.

Ba(OH)2 is an basic solution. It has more OH- ions than H+ ions. pOH should be calculated to find out its pH
The reaction is
Ba(OH)2 ⇒ Ba2+ (aq) + 2 OH-(aq)
One mole barium hydroxide releases 2 moles hydroxide ions.

Use that ratio to calculate molarity (M) of OH- ions [OH-]. The ratio is 1:2. 
0.10 M Ba(OH)2 release 2*0.10 M= 0.02 M OH- ions
[OH-]= 0.02
pOH= - log [OH-] = - log 0.02 = 1.7
Thats not the answer! We found pOH of the solution before titration.
pH and pOH relationship is shown by formula of pH+pOH= 14 
pH= 14-pOH
pH= 14-1.7= 12.3