Thank you for posting your question here. Below is the solution:
HNO3 --> H+ + NO3-
HNO3 = strong acid so 100% dissociation
** one doesn't need to find the molarity of water since it is the solvent
0M HNO3
1x10^-6M H3O+
1x10^-6M NO3-
1x10^-8M OH-.....the Kw = 1x10^-14 = [H+][OH-]
you have 1x10^-6M H+ so, 1x10^-14 / 1x10^-6 = 1x10^-8M OH-
1x10^-6 Ba(OH)2 = strong base, 100% dissociation
1x10^-6M Ba2+
2x10^-6M OH- since there are 2 OH- / 1 Ba2+
0M Ba(OH)2
5x10^-9M H3O+