From Henderson equation of acidic buffer solution we know,

**pH = pKa +log [A**^{-}]/[salt]

degree of ionization (∞) = √Kc/C = 3.4e-3

So,[CH_{3}COO^{-}] = C∞ = 3.4e-3 × 0.09 = 0.306e-3

So, pH = 4.7 + log [ 0.306e-3]/1.5 = 4.7 + log 0.0204 (log 0.0204 = -1.69)

= 4.7 - 1.69

= 3.01