Answer: (A) 15 degrees
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Step-by-step explanation:
With any parallelogram, the adjacent angles always add to 180 degrees.
(angle ADC) + (angle DCB) = 180
(angle ADC) + 120 = 180
angle ADC = 180 - 120
angle ADC = 60 degrees
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Angles 1 and 2 combine to form angle ADC by the angle addition postulate. This is just the idea of gluing smaller angles to form larger ones.
(angle 1) + (angle 2) = angle ADC
45 + (angle 2) = 60
angle 2 = 60-45
angle 2 = 15 degrees