18. \(4\sqrt2-\sqrt{32}+3\sqrt{128}\)

Упростим корни:

\(\sqrt{32}=4\sqrt2\), \(\sqrt{128}=8\sqrt2\).

\(4\sqrt2-4\sqrt2+3\cdot8\sqrt2=24\sqrt2\).

Ответ: \(24\sqrt2\)