Answer
16.8mL
Work Step by Step
To find the volume of the base needed to reach the equivalency point you simply use denominational analysis to convert from ml of Acetic acid to mL of Sodium hydroxide.
$\frac{20mL}{ }$ * $\frac{1L}{1000mL}$ * $\frac{0.105mol}{1L}$ * $\frac{1L}{0.125mol}$ * $\frac{1000ml}{1L}$ = 16.8mL
