two parallel lines are crossed by a transversal. if m∠6 = 123.5°, then m∠1 is 56.5°. 67.5°. 123.5°. 136.5°.

Explanation:

Step1: Identify angle - relationship

$\angle6$ and $\angle3$ are corresponding angles. Since the two lines are parallel, $m\angle6 = m\angle3=123.5^{\circ}$.

Step2: Use linear - pair property

$\angle1$ and $\angle3$ form a linear - pair. The sum of angles in a linear - pair is $180^{\circ}$. So $m\angle1 + m\angle3=180^{\circ}$.

Step3: Calculate $m\angle1$

$m\angle1=180^{\circ}-m\angle3 = 180^{\circ}- 123.5^{\circ}=56.5^{\circ}$.

Answer:

$56.5^{\circ}$