Thank you! I finally got it!
I used the fact that [OH-] ~= sqroot(Kb X [A-]), so I got [OH] from pOH and used the fact that since HA and NaOH were in equal volumes and concentrations, the [A-] would be half the concentration of HA. I got Ka from Kb (Ka= Kw/Kb)
In the end I got a Ka of about...