You have to use stoichiometry for the next part. Looking at the equation, you can see that for every 2 moles of H₂O, 1 mole of O₂ is produced. Convert from moles of O₂ to moles of H₂O using this relation.
I think you want to ask the complete ionic equation and net ionic equation. For complete ionic equation: 3Ba2+ + 6Cl- + 2Al3+ + 3SO42- -->3BaSO4 + 2Al3+ + 6Cl-. For net ionic equation: 3Ba2+ + 3SO42- -->3BaSO4.