Start by labeling the bottom side nearest to the lower 10degrees a.
Treat this as a constant, then start solving from there. Then just do tan=opposite/adjacent a bunch
Bottom left is a, that means the vertical is b=a*tan(20)
Now we want the bottom right. Call this c. tan(40)=c/b so tan(40)=c/a*tan(20) so c=tan(40)*a*tan(20)
Now we want the little half side of b. Call this d. a*tan(10)=d
atan(d/c)=x expand to atan(a*tan(10)/(tan(40)*tan(20)*a)) the a's cancel to give you 30 degrees unless i made a mistake somewhere
