Solution: From the meaning of the question: ∠ 1 = 30, ∠ 2 = 45, ∠ 3 = ∠ 4 = ∠ Abd = ∠ CDB = 90, CD = 18m.

∴ Quadrilateral CDBM is a rectangle∠ 2 =∠ CBM,

∴CD=BM=CM= 18

∫In Rt△ACM，tan ∠ 1 = amcm，

∴AM=CM？ tan30 = 18×33=63，

∵ in Rt△BCM, tan∠2=BMCM,

∴BM=CM？ tan45 = 18，

∴ AB = AM+BM = 18+63 ≈ 28 (m)。

Answer: Ginkgo trees are about 28 meters high.