∠∠PCD =∠PBC+∠BPC = m+40。 (the nature of the external angle of a triangle)

∴2∠pcd=2m+80；

Namely ∠ ACD = 2m+80;

∠∠ACD =∠ABC+∠BAC = 2m+∠BAC。

∴2m+80=2m+∠BAC,∠BAC=80 degree.

∴∠CAP=( 180 -∠BAC)/2=50。