Final answer:
The measure of angle m formed by two parallel lines and a transversal is 180° minus the angle between the parallel line and the transversal. Therefore, the correct answer is Option 2: 180° - m°y degrees.
Step-by-step explanation:
The question pertains to the measure of an angle m formed by two parallel lines a and b and a transversal intersecting them. If lines a and b are parallel and there is an angle m°y between them, then the measure of angle m is Option 2: 180° - m°y degrees.
This is because the angles on a straight line sum up to 180 degrees. If m°y is an angle formed between one of the parallel lines and the transversal, the adjacent angle on the same line would be supplementary to m°y, which means they add up to 180 degrees. Therefore, the measure of the other angle would get us back to a straight line if added to m°y, resulting in the correct answer being 180° - m°y degrees.