Answer:
∠ ABC = 38°
Explanation:
given AB = DB then Δ ABD is isosceles with base angles congruent, that is
∠ BDA = ∠ BAD = 71°
the sum of the 3 angles in Δ ABD = 180° , so
∠ ABC + 71° + 71° = 180°
∠ ABC + 142° = 180° ( subtract 142° from both sides )
∠ ABC = 38°