First, write a balanced equation and ensure the stoichiometry is in order:

 HCl +  NaOH →  NaCl  +  H\(_2\)O

Following the reaction above, the mole ratio is 1 : 1

Given:

Concentration of Acid, C\(_A\) = 0.12moldm\(^{-3}\),  Volume of Acid, V\(_A\) = ?

Concentration of Base, C\(_B\) = 0.20 moldm\(^{-3}\)  Volume of Base, V\(_B\) = 20cm\(^3\)

Using the relation, C\(_A\)V\(_A\) = C\(_B\)V\(_B\)

 V\(_A\) = \(\frac{C_BV_B}{C_A}\)

  = \(\frac{0.20 \times 20}{0.12}\)

  = 33.33cm\(^3\)