Let the north be y and the east be x.

∠AOB=∠AOy+∠yOB= 15+40=55

And OA is the bisector of ∠BOC.

that is

∠AOB=∠BOC=∠BOC/2

∠BOC=55*2= 1 10

that is

∠COx=∠xOy-∠AOC-∠AOy

=90-55- 15=20

That is, OC is 20 east of due north.

Linear BF

That is ∠xOF= 180-∠yOB-∠xOy.

= 180-90-40=50

∠COF =∠ COX +∠xOF

=50+20

=70