Answer:
Attached below is the missing figure
answer : ∠ABD = ∠AbC + ∠ CbD
Explanation:
when Line BC is drawn to divide ∠ABD equally
solving each angle :
∠ABD > ∠AbC also angle
∠ABD > ∠ CbD
∴ ∠ABD = ∠AbC + ∠ CbD
assuming ∠B = 60°
therefore ∠b = 60 / 30 = 30°