please ya kak. thanks

EC//AB
180°-70° = 110°
110°+20° = 130°
180°-130° = 50°

Garis EC sejajar dengan garis AB maka ∠AOD = ∠ECD = 70°
∠BOD = 180° - ∠AOD
∠BOD = 180 - 70°
∠BOD = 110°

∠BOD + ∠BDO + ∠OBD = 180°
110° + 20° + ∠0BD = 180°
∠OBD = 180° - 130° = 50°
Jawabannya b.

Semoga membantu.