Your topic should be: As shown in the picture, there is a lighthouse P on the sea, and there are reefs within 15km around it. A seagoing ship sailed from west to east at the speed of 40km/h, and at point A, it was found that lighthouse P was 60 east of its north, 18 minutes later, at point B, it was found that lighthouse P was 45 east of its north.

Solution: If P is the PC⊥AB of point C, it is obtained according to the meaning of the question.

AB=40×( 18/60)= 12，，∠PAB=90 -60 =30，

∠PBC=90 -45 =45，∠PCB=90，

∴PC=BC，

In Rt△PAC, tan 30 = PC/(ab+BC) = PC/(12+PC).

That is √3/3=PC/(PC+ 12), PC = 6 √ 3+6 > 15

The seagoing ship keeps moving forward, does not change direction, and there is no danger of hitting the rocks.