According to the meaning of the question, the triangle DPQ is an equilateral triangle (obtained by rotation, so DP=DQ, and because it has an angle of 60 degrees)

By connecting with equilateral triangles, it can be proved that these triangles are right triangles, including 30 degrees.

It's easy now! According to the given conditions, BD=3 and AB=9, BP = 6 (the right angle opposite to 30 degrees is half of the hypotenuse).

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