\(\left(3\sqrt{2}+\sqrt{6}\right).\sqrt{6-3\sqrt{3}}\) =\(\sqrt{2}\left(3+\sqrt{3}\right).\sqrt{6-3\sqrt{3}}\) =\(\left(3+\sqrt{3}\right).\sqrt{2.\left(6-3\sqrt{3}\right)}\) =\(\left(3+\sqrt{3}\right).\sqrt{12-6\sqrt{3}}\) =\(\left(3+\sqrt{3}\right).\sqrt{\left(3\right)^2-2.3.\sqrt{3}+\left(\sqrt{3}\right)^2}\) = \(\left(3+\sqrt{3}\right).\sqrt{\left(3-\sqrt{3}\right)^2}\) = \(\left(3+\sqrt{3}\right).|3-\sqrt{3}|\) =\(\left(3+\sqrt{3}\right).\left(3-\sqrt{3}\right)\) = \(9-3=6\)