I take it that 1.33E-10 is the average of Kb for acetic acid and you want to calculate Ka.
Ka*Kb = Kw = 1E-14
You know Kw and Kb, solve for Ka.
Now use the average value of Kb the base dissociation constant of acetate anion to calculate an average value for Ka, the acid dissociation constant of acetic acid.
Kb: 1.33x10^-10
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