Answer:
x = 30
Step-by-step explanation:
The sum of the exterior angle and interior angle of a polygon = 180°
Then the 2 unknown interior angles are
180 - 2x and 180 - (3x - 20) = 180 - 3x + 20 = 200 - 3x
The sum of the 4 interior angles of a quadrilateral = 360°
sum the 4 interior angles and equate to 360
2x + 2x + 10 + 180 - 2x + 200 - 3x = 360 , that is
- x + 390 = 360 ( subtract 390 from both sides )
- x = - 30 ( multiply both sides by - 1 )
x = 30
