Solution: according to the meaning of the question, ∠ bad = 45, ∠ BCD = 30, AC=20m.

In Rt△ABD, AB=BD is obtained from ∠ bad = ∠ BDA = 45.

In Rt△BDC, tan∠BCD=, we get.

∫BC-AB = AC，

∴ ,

∴ ,

A: "A little."