Answer:
y = 43°
Step-by-step explanation:
The unknown angle x inside the quadrilateral is adjacent to 80° and sum to 180° , then
x = 180° - 80° = 100°
The sum of the 4 interior angles of a quadrilateral = 360°
sum the 4 angles and equate to 360°
y + 145° + 72° + 100° = 360° , that is
y + 317° = 360° ( subtract 317° from both sides )
y = 43°
