[munchkiness]

How do i start calculating the pH of a barium hydroxide solution?

I've already worked out the ion concentrations from an earlier question.

[enahs]

Kw = [H⁺][OH^-] = 10(10^-14)

Correct? Do not take my word for it. Verify it. Learn it!

You know everything but H⁺, you can solve for it, and then plug that into your pH equation.

Alternatively. You can calculate the pOH, -log([OH-], and take that away from 14.
I.E.
pH = 14 - ( -log ([OH^-]) )

Right? Can you reason these out? This all comes from the equilibrium constant of water and then doing math.