All give you a good starting point.
Let angle b = x
Now you can get every angle there in terms of x.
Start with the most obvious and work from there.
It is not all that hard.
eventually you will have 2 or 3 angles all in terms of x that add to give 180 degrees.
Then you will just have a little equation to solve to get x.
When you finish you should check that it works,
Please no one else give a full answer.
Jenny, you can interact with me if you need/want to.