[tex]a)20 \sqrt{6} \times (3 \sqrt{2} - 2 \sqrt{3}) + 5 \sqrt{6} \times (6 \sqrt{3} - 7 \sqrt{2}) = \\ \\ 120 \sqrt{3} - 120 \sqrt{2} + 90 \sqrt{2} - 70 \sqrt{3} = \\ \\ (120 \sqrt{3} - 70 \sqrt{3}) + ( - 120 \sqrt{2} + 90 \sqrt{2}) = \\ \\ 50 \sqrt{3} - 30 \sqrt{2} [/tex]
