Let y be the missing interior angle of the quadrilateral. So angle y is adjacent to angle x.
Recall that the sum of all four angles of any quadrilateral is 360, so, 40+80+110+y = 360 230+y = 360 230+y-230 = 360-230 ... subtract 230 from both sides y = 130
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Angle y and angle x form a straight angle. The two angles add to 180 degrees x+y = 180 x+130 = 180 x+130-130 = 180-130 ... subtract 130 from both sides x = 50
