I dissolved 4g of solid NaOH in 200mL of water. I converted grams of NaOH to moles by 4g/40g/moles= 0.1moles.

Question

I calculated the concentration of NaOH by 0.1/(200mL/1000L)= 0.5 moles/L.
I now have to record the expected mass of benzoic acid required to react in stoichiometric proportion with 20mL of the NaOH solution. Not sure about this part.

Answer 1

First, you write the equation.
PhCOOH + NaOH ==> PhCOONa + H2O

So you used 20 mL of 0.5 mole/L which means you used 0.50 x 0.02 = 0.01 mole NaOH.
Since the reaction is a 1:1 mole ratio, it will require 0.01 mole benzoic acid. How many grams is 0.01 mole benzoic acid? You know benzoic acid is about 122 g/mol so 0.01 moles would be about 1.22 g. You can do it exactly.