OG Quant Review: DS, Chapter 5.5, Problem 117 wrong?

Has anyone see this happen? I think their answer is wrong.. They have a triangle ABC, And a point D on AC. BDC = BCD = 2xdegree. What is BC? 1) AD = 6 2) x = 36 They say AD = 6 is sufficient to know the length of BC. I dont think so.. We know BD = BC, because angles are equal.. but I dont know how d...