I was working on a geometry problem relating to the angle bisectors of triangles :
In triangle $\Delta ~ABC$, $~∠A=40°,~ ∠B=20°,~$ and $~AB − BC = 4~$. Find the length of angle bisector from $~∠C~$.
I was able to figure out a majority of the angle measures, but I was unable to utilize the information about the side lengths to find the angle bisector.
Does anyone what method I have to use to solve this?