In mixture (before dilution )
${\displaystyle \left[C{H}_{3}COOH\right]=\frac{0.01\times 100}{300}=\frac{0.01}{3}M}$
${\displaystyle \left[C{H}_{3}COONa\right]=\frac{0.02\times 200}{300}=\frac{0.04}{3}M}$
${\displaystyle pH=p{K}_a+\log .\frac{\left[\text{salt}\right]}{\left[\text{acid}\right]}}$
${\displaystyle =4.74+\log .\frac{004}{3}\times \frac{3}{0.01}}$
${\displaystyle =4.74+\log 4}$
${\displaystyle =4.74+0.60=5.34}$
On dilution , no change in pH will take place.
pH (before) = pK_a + log 4 =5.34

Dilution has no effect on pH of buffer.