In short, angle 1 and angle 7 are congruent because they are corresponding angles formed by parallel lines cut by a transversal.
Identify a transversal line that intersects both sets of parallel lines.
Identify the corresponding angles on each side of the transversal. Corresponding angles are angles that are in the same relative position on opposite sides of the transversal. In this case, angle 1 and angle 7 are corresponding angles.
Since lines 1 and 3 are parallel, and the line is a transversal, we know that angle 1 and angle 7 are congruent by the corresponding angles postulate. This postulate states that if two parallel lines are cut by a transversal, then the corresponding angles are congruent.