< AO D=?

The inscribed angle subtended by arc AB is 15 degrees. The central angle subtended by the same arc is twice the inscribed angle, so ∠AOB = 2 * 15° = 30°. Since AD and BC are diameters, ∠AOD and ∠BOC are vertically opposite angles. Also, ∠AOD and ∠BOC are supplementary to ∠AOB and ∠COD respectively. Since AD and BC are diameters, ∠AOB = ∠COD and ∠AOD = ∠BOC. The sum of angles around the center is 360°. Thus, 2 * ∠AOB + 2 * ∠AOD = 360°. Substituting ∠AOB = 30°, we get 2 * 30° + 2 * ∠AOD = 360°, which simplifies to 60° + 2 * ∠AOD = 360°. Therefore, 2 * ∠AOD = 300°, and ∠AOD = 150°.