Answer: 60 (choice D)
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Step-by-step explanation:
Let y be the angle just to the left of angle x. Angle x and angle y are adjacent.
Since line a is parallel to line b, this means y = 120 because the 120 degree angle and angle y are alternate interior angles.
Then we can say:
x+y = 180
x+120 = 180
x = 180-120
x = 60
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An alternative method:
Let w be the angle just above angle x
The angle marked "120 degrees" and angle w are corresponding angles. They are congruent if and only if line a is parallel to line b.
This makes w = 120
Solving w+x = 180 leads to x = 60 similar to the previous set of steps.
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Side note:
The 115 degree angle is never used. It was probably put in there as a distraction.