4) 3√20 + 5√45 − 2√80

Упрощаем корни: \(\sqrt{20}=2\sqrt{5}\), \(\sqrt{45}=3\sqrt{5}\), \(\sqrt{80}=4\sqrt{5}\).

\(3\sqrt{20}+5\sqrt{45}-2\sqrt{80}=6\sqrt{5}+15\sqrt{5}-8\sqrt{5}=13\sqrt{5}\).

Ответ: \(13\sqrt{5}\).