NaOH should be added to 45.0 ml of HCL to completely neutralize the acid

Well, you need to add 45.0⋅mL of your standard NaOH solution precisely ...

Explanation:

And first we represent the reaction by an equation:

HCl (aq) + NaOH (aq) →NaCl (aq) + H2O (l)

And thus there is 1:1 stoichiometry.

We use the relationship Molarity=Moles of soluteVolume of solution.