Challenge Question:

Triangle $\displaystyle ABC$ is an isosceles triangle with base $\displaystyle BC$ , the included angle of $\displaystyle A $ is $\displaystyle 20$ degree . A point $\displaystyle D$is marked off on side $\displaystyle AC $ such that $\displaystyle AD = BC $ . What is the angle of $\displaystyle ABD $ ?

Moderator edit:This is now an approved challenge question.