Let's simplify each expression step-by-step.

Expression A:

$A = 3\sqrt{8} - \sqrt{32} + \sqrt{72} + 3\sqrt{28}$

1. Simplify each term:

   • $3\sqrt{8} = 3 \times 2\sqrt{2} = 6\sqrt{2}$
   • $\sqrt{32} = 4\sqrt{2}$
   • $\sqrt{72} = 6\sqrt{2}$
   • $3\sqrt{28} = 3 \times 2\sqrt{7} = 6\sqrt{7}$

2. Substitute and combine like terms: $A = 6\sqrt{2} - 4\sqrt{2} + 6\sqrt{2} + 6\sqrt{7} = 8\sqrt{2} + 6\sqrt{7}$

Expression B:

$B = 2\sqrt{80} - \sqrt{45} + \sqrt{20}$

1. Simplify each term:

   • $2\sqrt{80} = 2 \times 4\sqrt{5} = 8\sqrt{5}$
   • $\sqrt{45} = 3\sqrt{5}$
   • $\sqrt{20} = 2\sqrt{5}$

2. Substitute and combine like terms: $B = 8\sqrt{5} - 3\sqrt{5} + 2\sqrt{5} = 7\sqrt{5}$

Expression H:

$H = \sqrt{36a} + \sqrt{64a} - 2\sqrt{16a}$

1. Simplify each term:

   • $\sqrt{36a} = 6\sqrt{a}$
   • $\sqrt{64a} = 8\sqrt{a}$
   • $2\sqrt{16a} = 2 \times 4\sqrt{a} = 8\sqrt{a}$

2. Substitute and combine like terms: $H = 6\sqrt{a} + 8\sqrt{a} - 8\sqrt{a} = 6\sqrt{a}$

Expression G:

$G = \sqrt{2\sqrt{45}} - 3\sqrt{20}$

1. Simplify each term:
   • (\sqrt{45} = 3\