For ethan hunt. pls check whether this is a correct answer or not.

Here, Equation: 2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O

We know, Concentration (c) = Number of moles(n) / Volume (v)

Substitute the given values, 
0.02 = n / 0.3   [ 300 mL = 0.3 L ]
n = 0.3 * 0.02
n = 0.006

Now, According to stoichiometry, There is 1 Molecule of Sodium sulfate produces for every 2 molecules of NaOH.

So, Number of Moles of Na₂SO₄ = 0.006/2 = 0.003

Given mass = Molar mass * Number of moles
M = 142.04 * 0.003
M = 0.426 g

In short, Your Answer would be: 0.426 g

Hope this helps!