The correct option is A 30
In △ABD and △CDB,
DA = BC (given)
BD = DB (common side)
∠ABD=∠CDB=90∘
Hence, △ABD≅△CDB
(by RHS criteria for congruence of triangles)
So, ∠DAB=∠BCD=60∘
By ange sum property of triangle,
∠BDA+∠ABD+∠DAB=180∘
∠BDA=180∘−∠ABD+∠DAB
⟹∠BDA=180∘−(90∘+60∘)
⟹∠BDA=180∘−150∘
⟹∠BDA=30∘