Answer:
x = 10
Step-by-step explanation:
The sum of the interior angles of a quadrilateral = 360°
Sum the angles and equate to 360
9x + 15 + 85 + 90 + 80 = 360, that is
9x + 270 = 360 ( subtract 270 from both sides )
9x = 90 ( divide both sides by 9 )
x = 10
