Triangles A B C and B C D are shown sharing the same side B C with sides A B and C D both being three point nine units. Sides B D and A C are both four units. Angle D C B is x degrees. Angle C A B is one hundred degrees. Angle A C B is thirty degrees. \[100^{\circ}\] \[30^\circ\] \[3.9\] \[4\] \[A\] \[B\] \[C\] \[x^\circ\] \[3.9\] \[4\] \[D\] \[x = \]