45. Solving a chemistry problem

338. A portion of ammonium sulfate was dissolved in a volumetric flask with a capacity of 100 cm3. 50 cm3 of 0.1122 M sodium hydroxide solution was added to 20 cm3 of the resulting solution and heated until complete removal of NH3. The alkali residue was titrated with 18 cm3 of HCl solution. Note that 20 cm3 NaOH solution is equivalent to 21 cm3 HCl solution. Calculate what mass of ammonium sulfate was contained in the initial solution.