Answer: C. 84
Step-by-step explanation:
In triangles ABD y BCD:
- AD=CD
- Angle BAD = angle BCD
- BD common side
THEN the triangles are equal because they have two sides and the angle opposite the longest side respectively equal.
CBD = ABD = 42 because the triangles ABD y BCD are equal
ABC = CBD+ABD = 42+42= 84
