In the figure, transversal t intersects the parallel lines a and b.

(this is where the screenshot would be). the theorem by which they are congruent is the

(a) alternate exterior angles theorem
(b) alternate interior angles theorem
(c) vertical angles theorem
d) same side interior angles theorem

Lines a and b are parallel, and line t is a transversal.
Notice that angles 2 and 7 are on the outside of the parallel lines, and they are on different sides of the transversal.
Angles 2 and 7 are alternate exterior angles.

The answer is (a) alternate exterior angles theorem.

It is by the "alternate exterior angles theorem" that angles 2 and 7 are congruent.