Test analysis: By observing the graph, it can be concluded that △ACM is a right triangle, △BCM is a right triangle, and quadrilateral CDBM is a rectangle. Then, in Rt△BCM and Rt△ACM, the lengths of BM and AM can be obtained by trigonometric function values of special angles.

Problem analysis: As shown in the figure,

Judging from the meaning in the title: ∠ 1 = 30, ∠ 2 = 45, ∠ 3 = ∠ 4 = ∠ Abd = ∠ CDB = 90, DB = 12m.

∴ cm = 12m

In Rt△ACM,

∴ ;

In Rt△BCM, BM=CM= 12.

∴AB=AM+BM= (male).

Test center: solve the application of right triangle-elevation angle and depression angle.