all angles in a quadrilateral add to 360
x is supplementary to that other angle, call it y
the angles inside are 40, 80, 110 and y
40+80+110+y=360
230+y=360
minus 230 both sides
y=130
that is supplementary to x (adds to 180)
x+y=180
x+130=180
minus 130 both sides
x=50
x=50 degrees