According to known available ∠ACB=36? ; So BCD = 6? ;
Sin∠BCD=BD/BC, then BD=54*Sin6? ;
Cos∠BCD=CD/BC, then CD=54*Cos6? ;
Tan∠ACD=AD/CD=(AB+BD)/CD
So CD*tan∠ACD-BD=AB=54*Cos6? *tan42? -54*Sin6?
=54*Sin(2*42? )sin42? /cos42? -54*cos(2*42? )
=54*2sin42? cos42? sin42? /cos42? -54*[ 1-2(sin42? )^2]
=54*2(sin42? )^2-54+54*2(sin42? )^2
=2 16*(sin42? )^2-54
Ship speed =AB/2 hours