Since we already have the balanced reaction, let's start by applying

M =

moles/L

0.320 M NaOH =

x moles NaOH /0.0342 L NaOH

= 0.01094 moles NaOH


Now, we use our reaction equation to do a mole to mole ratio

0.01094 moles NaOH

(1 mole H₂SO₄)₃ / (2 mole NaOH)

= 0.00547 moles H₂SO₄


We know both H₂SO₄ Molarity and moles, hence we can find L

0.186 M H₂SO₄

(0.00547 mole H₂SO₄)/ (L H₂SO₄)

= 0.0294 L H₂SO₄


The volume needed is 29.4 mL