Answer:
(5x+40)+x+2(2x+20)=360
5x+40+x+4x+40=360
10x+80=360
10x=360-80
10x=280
x=28°
substitute x=28° into (5x+40)
=140+40= 180
therefore line Ac is the diameter of a he circle because a diameter divides a circle into 2 equal part and the angle on the line is 180° showing that the circle is on a straight line