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Hmm, I think in the question there is used wrong symbol. It should be \(m\angle 1=55^{\circ}\)Then\(m\angle12=m\angle1=55^{\circ} \Rightarrow D\)
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