$\begin{align}  & \text{Using the sine rule} \\ & \frac{10cm}{\sin {{30}^{\text{o}}}}=\frac{x}{\sin {{60}^{\text{o}}}} \\ & x=\frac{10cm\times \sin {{60}^{\circ }}}{\sin {{30}^{\circ }}}=\frac{10cm\times \tfrac{\sqrt{3}}{2}}{\tfrac{1}{2}} \\ & x=\frac{10\times \sqrt{3}\times 2}{2}=10\sqrt{3}cm \\\end{align}$