Hmm, I think in the question there is used wrong symbol. It should be [tex]m\angle 1=55^{\circ}[/tex] Then [tex]m\angle12=m\angle1=55^{\circ} \Rightarrow D[/tex]
The Answer is D because number 12 angle is acute not obtuse and 12 angle and 1 angle are vertical angles and vertical angles are always the same number of degrees
