They are formed on the outside of the parallel lines and lie on opposite sides of the transversal.
Also, when a transversal intersects parallel lines, alternate exterior angles are congruent. Lines a and b are parallel and the given angle and ∠8 are alternate exterior angles. This means that these angles are congruent.
Congruent angles have the same measure, so the measure of ∠8 is 140^(∘).
