Угол С = 180° - 60° - 45° = 75°
По теореме синусов: $$ \frac{BC}{\sin A} = \frac{AC}{\sin B} $$
$$ \frac{76}{\sin 60°} = \frac{AC}{\sin 45°} $$
$$ AC = \frac{76 \cdot \sin 45°}{\sin 60°} = \frac{76 \cdot \frac{\sqrt{2}}{2}}{\frac{\sqrt{3}}{2}} = \frac{76 \sqrt{2}}{\sqrt{3}} = \frac{76 \sqrt{6}}{3} $$
Ответ: $$ \frac{76 \sqrt{6}}{3} $$