По теореме синусов:
\( \frac{AC}{\sin B} = \frac{BC}{\sin A} \)
\( \frac{AC}{\sin 60^{\circ}} = \frac{4\sqrt{6}}{\sin 45^{\circ}} \)
\( AC = \frac{4\sqrt{6} \cdot \sin 60^{\circ}}{\sin 45^{\circ}} \)
\( AC = \frac{4\sqrt{6} \cdot \frac{\sqrt{3}}{2}}{\frac{\sqrt{2}}{2}} \)
\( AC = \frac{4\sqrt{18}}{\sqrt{2}} \)
\( AC = 4\sqrt{\frac{18}{2}} \)
\( AC = 4\sqrt{9} \)
\( AC = 4 \cdot 3 \)
\( AC = 12 \)
Ответ: 12