Question

lines m and n are parallel. find the measure of ∠a. m∠a = ?°

Explanation:

Step1: Find the supplementary angle

When two lines are parallel and cut by a transversal, the sum of an angle and its consecutive - interior angle is $180^{\circ}$. Let the angle adjacent to $\angle a$ be $112^{\circ}$.

Step2: Calculate $\angle a$

Use the formula $m\angle a=180^{\circ}-112^{\circ}$.
$$m\angle a = 180 - 112=68^{\circ}$$

Answer:

$68$