4. \((\sqrt{18}+\sqrt{2})\cdot\sqrt{2}\)

Упростим корень: \(\sqrt{18}=3\sqrt{2}\).

\((\sqrt{18}+\sqrt{2})\sqrt{2}=(3\sqrt{2}+\sqrt{2})\sqrt{2}=4\sqrt{2}\cdot\sqrt{2}=4\cdot2=8\).

Ответ: 8