9514 1404 393
Answer:
75°
Step-by-step explanation:
Angles CAB and DBA are consecutive interior angles where transversal AB crosses parallel lines BD and AC. So, those angles are supplementary.
∠DBA +∠CAB = 180°
∠DBA +30° = 180°
∠DBA = 150°
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Angle ABC is a base angle of isosceles triangle ABC, so has measure ...
∠ABC = (180° -30°)/2 = 75°
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Angle DBC is the difference of angles DBA and CBA, so is ...
∠DBC = ∠DBA -∠CBA
∠DBC = 150° - 75°
∠DBC = 75°
