Angle ABC = DEC
angle C = 55 degrees
angle B = 2x
angle D = 65 degrees
Angle on a straight line = 180 degrees
2x + 55 + 65 = 180
isolate 2x
2x + 120 = 180
2x = 180 -120
2x = 60
divide both sides by 2
2x/2 = 60/2
x = 30 degrees
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