In a triangle ABC, BC is produced to D so that CD = AC. If ∠BAD = 111° and ∠ACB = 80°, then the measure of ∠ABC is:

Answer: Option D

According to question,

Given :
AC = CD
∠BAD = 111°
∠ACB = 80°
∴ ∠ACD = 180° - 80°
∠ACD = 100°
In isosceles triangle ACD
   ∠ACD + ∠CAD + ∠ADC = 180°
   2∠CAD = 180° - 100°
   ∠CAD = 40°
∴ ∠CAB = 111° - 40° = 71°
∴ ∠ABC = 180° - 71° - 80°
   ∠ABC = 29°