∠ABD+∠DBE+∠EBC=180∘We know that ∠ABD=60∘ and that ∠EBC=90∘, so we can substitute in those values to create an equation with a single variable that we can then solve for.​60∘+∠DBE+90∘=180∘150∘+∠DBE=180∘∠DBE=30∘​The correct answer is A.