Na2SO4 + 2HCl ==> 2NaCl + H2SO4
mols Na2SO4 = M x L = estimated 16 but you do it more accurately.
mols HCl = M x L = estimated 21.
Now use the coefficients in the balanced equation to convert mols of each into mols NaCl.
For Na2SO4 that is estimated 16*2 = estimated 32g
For HCl that is 21 mols x 1 = estimated 21.
You two values for mols NaCl and i is obvious one of them is wrong. In limiting reagent problems the smaller values if ALWAYS the correct value to choose.
Now convert mols NaCl to g. g mols x molar mass.