...........Al(OH)3 ==> Al^3+ + 3OH^-
I.........solid.........0.......0
C.........solid.........x.......3x
E.........solid.........x.......3x
Substitute the E line into the Ksp expression for Al(OH)3 and solve for x = (Al^3+). Convert that to OH^-, change to H^+ and convert to pH.
Then use the Henderson-Hasselbalch equation. pH = pKa + log (base)/(acid)
The pH from part 1 goes in for pH here, pKa is that for acetic acid and solve fr (base)/(acid) ratio.