Answer:
Alternate interior angles theorem
Explanation:
The question wants you to prove that angle 4 and angle 5 are congruent to each other.
Angle 4 and angle 5 are alternate congruent angles.
Alternate interior angles are congruent to each other, as stated by the alternate interior angles theorem.
To understand this better, you can look up this theorem, and look at the pictures given for a visual representation.