Используем теорему синусов:
$$\frac{AC}{sin(∠ABC)} = \frac{AB}{sin(∠ACB)}$$
$$\frac{4\sqrt{2}}{sin(45°)} = \frac{6}{sin(∠ACB)}$$
$$sin(∠ACB) = \frac{6 \cdot sin(45°)}{4\sqrt{2}} = \frac{6 \cdot (\frac{\sqrt{2}}{2})}{4\sqrt{2}} = \frac{3\sqrt{2}}{4\sqrt{2}} = \frac{3}{4}$$
Ответ: 3/4