The answer is 16.
We have. 2(NH₄)₂SO₄. In NH₄ there are 4 atoms of hydrogen (H). However, in one molecule of (NH₄)₂SO₄, because of subscript 2, there are 2 · 4 = 8 atoms of hydrogen. Further, there are two molecules of (NH₄)₂SO₄ - 2(NH₄)₂SO₄, therefore, there are in total 16 atoms: 2 · 8 = 16
