Answer:
∠ ADC = 110°
Step-by-step explanation:
∠ CDE = 90° ( angle between perpendicular lines ) , then
∠ CDB + ∠ BDE = 90°
∠ CDB + 20° = 90° ( subtract 20° from both sides )
∠ CDB = 70°
∠ ADC and ∠ CDB are adjacent angles on a straight line and sum to 180° , so
∠ ADC + ∠ CDB = 180° , that is
∠ ADC + 70° = 180° ( subtract 70° from both sides )
∠ ADC = 110°
