[Mariposa]

 I do not know where to ask this question and I need to know how to find this pH

[AWK]

You should know a molar concentration of (NH₄)₂SO₄ instead od percent concentration. Sulfuric acid will react with ammonium sulfate forming hydrogen ammonium sulfate and the final mixture will contain ammonium sulfate and hydrogen ammonium sulfate ((NH₄)₂SO₄ and NH₄HSO₄). This mixture will work as buffer solution based on the second acidity constant of sulfuric acid (quadratic equation!).