Answer: 120
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Explanation:
Refer to the diagram below.
I've added the angle 40 degrees shown in red. This is possible since we have a pair of congruent alternate interior angles (due to the parallel lines).
The three angles 20, x and 40 on the left hand side all combine to form a straight line of 180 degrees.
20+x+40 = 180
x+60 = 180
x = 180-60
x = 120
