Online Geometry Problem 832: Quadrilateral, Isosceles triangle, 70-70-40 degrees, Congruence, Auxiliary lines, Equilateral triangle. Level: High School, SAT Prep, College, Mathematics Education

The figure below shows a quadrilateral ABCD with AD = BC, angle BAD = angle ADB = 70 degrees, and angle BDC = 20 degrees. Find the measure of angle CBD. Problem submitted by Charles T.