Answer
$pH = 7.60$
Work Step by Step
1. Calculate the pKa Value
$pKa = -log(Ka)$
$pKa = -log( 2.9 \times 10^{- 8})$
$pKa = 7.54$
2. Using the Henderson–Hasselbalch equation:
$pH = pKa + log(\frac{[Base]}{[Acid]})$
$pH = 7.54 + log(\frac{0.155}{0.135})$
$pH = 7.54 + log(1.147)$
$pH = 7.54 + 0.06$
$pH = 7.60$
