Have ∠CAB=45？ ，∠ACB= 180？ -60? = 120?

∠ABC=60？ -45? = 15? ,

Draw a conclusion from sine theorem

40/sin 15？ =BC/sin45？

BC=40*sin45？ /sin 15？

Sin 15 again? =sin(45？ -30? )=(√ 6-√ 2)/4.

BC=(40*√ 2/2)/[(√ 6-√ 2)/4]

=40√3-20√2(mim)。

∴ At this time, the distance between the cargo ship and lighthouse B is 40√3-20√2(mim).