There are two parellel lines and one transversal cutting across them. One angle is known, but there are two others and are not found. The question is to find the measure of the unknown angles.

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Now, given that there are two parallel lines are transversed by another line, then the angles would ook like the figure below.

Now, if we only know the measurement of one angle, say, angle A, given the principles of angles, we know that corresponding angles are equal. This means that

1. angle A = angle C

2. angle B = angle D

We also know that to get the measurement of Angle B, we only need to subtract the measurement of Angle A from 180 degrees since Angle A and Angle B are in a straight line, therefore

Angle A + Angle B = 180 degrees

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