$\begin{align}  & A=\tfrac{1}{2}rq\sin \theta  \\ & 12\sqrt{3}=\tfrac{1}{2}\times 8\times q\sin 6{{0}^{\circ }} \\ & 12\sqrt{3}=4q\times \frac{\sqrt{3}}{2} \\ & q=6cm \\\end{align}$