Answer:
x = 15
Step-by-step explanation:
The sum of the 4 angles in a quadrilateral = 360°
The fourth angle in the quadrilateral lies on a straight angle with x + 100, thus the angles are supplementary, hence
fourth angle = 180 - (x + 100) = 180 - x - 100 = 80 - x
Sum the 4 angles and equate to 360
2x + 55 + 80 - x + 90 + 120 = 360 ← simplify left side
x + 345 = 360 ( subtract 345 from both sides )
x = 15
