Answer: 55
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The 125 degree angle and angle 6 are supplementary. This is because of the same side interior angles theorem.
Let x be the measure of angle 6. Add this to 125, set the sum equal to 180, and solve for x.
x+125 = 180
x = 180-125
x = 55
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Or you could approach it this way:
y = measure of angle 2
y+125 = 180
y = 55
angle 6 = angle 2 (corresponding angles)
angle 6 = 55 degrees
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Yet another way you could solve:
z = measure of angle 3
z+125 = 180
z = 55
angle 6 = angle 3 (alternate interior angles)
angle 6 = 55 degrees
A similar approach using alternate interior angles would involve angle 5 = 125, and then noticing that x+125 = 180 solves to x = 55