Answer: x = 7.2
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Explanation:
As shown in the diagram (see attached image below), the red interior angles are
180-10x
180-15x
180-20x
180-5x
Each of those expressions is in the form 180-E, with E as the exterior angle. Add up the interior angles. Set the sum equal to 360 and solve for x. For any quadrilateral, the four interior angles always add to 360.
(angle1)+(angle2)+(angle3)+(angle4) = 360
(180-10x) + (180-15x) + (180-20x) + (180-5x) = 360
(180+180+180+180)+(-10x-15x-20x-5x) = 360
720-50x = 360
-50x = 360-720
-50x = -360
x = -360/(-50)
x = 36/5
x = 7.2
