If , find .
Let represent the point where and intersect.
Step 1: Find .
The sum of a triangle's interior angle measures is , so we can find by subtracting 's two other angles measures from .
Step 2: Find .
and are alternate interior angles of a line segment and parallel ray crossed by a transversal, so they are equal in measure.
Step 3: Find .
and form a straight angle, so they are supplementary angles (with a sum of ). Therefore, we can find by subtracting from .