Same-Side Interior Angles are angles that are on the interior of the parallel lines and lie on the same side of the transversal.
In the figure below, parallel lines \(m\) and \(n\) are cut by the transversal \(t\).
The pairs of the same-side interior angles are as follows:
\(\angle{1}\) and \(\angle{4}\)
\(\angle{2}\) and \(\angle{3}\)
Since the transversal intersected parallel lines, the alternate exterior angles are supplementary.