По теореме синусов:
$$\frac{AB}{\sin C} = 2R$$
$$R = \frac{AB}{2\sin C}$$
$$R = \frac{14\sqrt{2}}{2\sin 135^{\circ}}$$
$$R = \frac{14\sqrt{2}}{2\sin (180^{\circ}-45^{\circ})}$$
$$R = \frac{14\sqrt{2}}{2\sin 45^{\circ}}$$
$$R = \frac{14\sqrt{2}}{2 \cdot \frac{\sqrt{2}}{2}}$$
$$R = \frac{14\sqrt{2}}{\sqrt{2}}$$
$$R = 14$$
Ответ: 14