Answer:
∠ 4 = 80°
Step-by-step explanation:
∠ 5 and 100° are vertical angles and are congruent , so
∠ 5 = 100°
∠ 4 and ∠ 5 are same- side interior angles and sum to 180° , that is
∠ 4 + ∠ 5 = 180°
∠ 4 + 100° = 180° ( subtract 100° from both sides )
∠ 4 = 80°
