B2. 2) ∠MON : ∠BON = 4 : 15, ∠MON, ∠BON, ∠AON - ?

1. ∠MON : ∠BON = 4 : 15. Let ∠MON = 4x, ∠BON = 15x.
2. ∠AON = ∠MON + ∠BON = 4x + 15x = 19x.
3. If ∠AON = 30°, then 19x = 30°, x = 30°/19. ∠MON = 4 * 30°/19 = 120°/19, ∠BON = 15 * 30°/19 = 450°/19.