Answer:
Given: [tex]r || s[/tex] and q is a transversal.
Alternative Interior Angle states that a pair of angles on the inner side of each of those two lines but on opposite sides of the transversal are equal.
By alternative interior angle;
[tex]\angle 3 \cong \angle 6[/tex]
Definition of Congruent angles are angles that have the same degree of measurement.
Therefore, [tex]m\angle 3 = m\angle 6[/tex] [By definition of Congruent] .....[1]
Linear Pair states that a pair of adjacent angles formed when two lines are intersect.
therefore, [tex]\angle 4[/tex] and [tex]\angle 3[/tex] are a linear pair. [by definition of linear pair]
Two angles of linear pairs are always supplementary , which means their measure are add up to 180 degree.
By the definition of supplementary angles, [tex]m\angle 4 + m\angle 3 = 180^{\circ}[/tex] .....[2]
Substitute equation [1] in [2] we get,
[tex]m\angle 4 +m\angle 6 =180^{\circ}[/tex]
By the definition of supplementary angles,
[tex]\angle 4[/tex] is supplementary to [tex] \angle 6[/tex] Hence proved!