Ответ:

$$\frac{\sqrt{720} \cdot \sqrt{15}}{\sqrt{600}} = \frac{\sqrt{720 \cdot 15}}{\sqrt{600}} = \sqrt{\frac{720 \cdot 15}{600}} = \sqrt{\frac{72 \cdot 15}{60}} = \sqrt{\frac{6 \cdot 12 \cdot 15}{5 \cdot 12}} = \sqrt{6 \cdot 3} = \sqrt{18} = \sqrt{9 \cdot 2} = 3\sqrt{2}$$.
Ответ: 3) $$3\sqrt{2}$$