Answer:
To find x you need to divide polygon into triangles
The formula : "the sum of exterior angles=360°" is false for concaved polygons
Explanation:
α = 180° - 135° = 45°
β = 180° - 120° = 60°
γ = 180° - 60° = 120°
δ = 180° - x
ε = 180° - 80° = 100°
If we divide the pentagon into five triangles then:
5•180° = α + β + γ + δ + ε + 4x
900° = 45° + 60° + 120° + x + 100° + 4x
900° = 325° + 5x
5x = 575°
x = 115°
60° + 120° + 135° + 80° + 115° = 510° ≠ 360°