number of mole (NaOH)= 1.85 mol
Using mole ratio
n(Na2SO4)/n(NaOH)= 1/3
So number of mole of Na2SO4 is the number of mole of NaOH multiplied by 1/3 which equals 0.616 (approx.)
Then to find mass we use
Mass(in grams)= number of mole of compound (Na2SO4) multiplied by the Molar mass of our compound molar mass (Na2SO4) =142.04
m= n X Mr
m= 0.616 x 142.04
=87.59g