61. \((\sqrt{75}-\sqrt{48})\cdot\sqrt{12}\).

Упростим корни: \(\sqrt{75}=5\sqrt{3}\), \(\sqrt{48}=4\sqrt{3}\), \(\sqrt{12}=2\sqrt{3}\).

\((5\sqrt{3}-4\sqrt{3})\cdot2\sqrt{3}=\sqrt{3}\cdot2\sqrt{3}=2\cdot3=6\).

Ответ: 6.