If BD=DC that means triangle CDB is isosceles triangle and the measure of angles ∡CDB and ∡BCD is the same
∡CDB=∡BCD=70°
The angles ∡ADB and ∡CDB are adjacent and suplementary angles
It means ∡ADB + ∡CDB = 180°
∡ADB = 180° - ∡CDB
∡ADB = 180° - 70°
∡ADB = 110°
