$\begin{align}  & \angle BDC+\angle BDA=180{}^\circ \text{  }\!\!\{\!\!\text{ Sum }\angle \text{s on a straight line }\!\!\}\!\!\text{ } \\ & \text{65}{}^\circ +\angle BDA=180{}^\circ  \\ & \angle BDA=115{}^\circ  \\ & \angle BDA+\angle BAD+\angle ABD=180{}^\circ \text{ (Sum }\angle \text{s in a }\vartriangle \text{ }\!\!\}\!\!\text{ } \\ & 115{}^\circ +50{}^\circ +x=180{}^\circ  \\ & x=15{}^\circ  \\\end{align}$