In the adjoining diagram the length of PR is :

From figure,

⇒ sin 60° = $\frac{QR}{PR}$

⇒ $\frac{\sqrt{3}}{2} = \frac{9}{PR}$

⇒ PR = $\frac{9 \times 2}{\sqrt{3}} = 3\sqrt{3} \times 2 = 6\sqrt{3}$ cm.

Hence, Option 2 is the correct option.