Answer:
Explanation:
Remark
The diagram makes the line AB look like it is tilted a bit to the right. I'm going to assume that isn't right. AB extended is a straight line. ADC is supplementary to the 80o angle.
Solution
<ADC + 80o = 180 They are on the same straight line
<ADC = 180 - 80 Subtract 80 from both sides
<ADC = 100o
Opposite angles of a cyclic quadrilatral are supplementary
<ADC + <ABC = 180 Property of cyclic quadrilaterals
100 + <ABC = 180 Subtract 100 from both sides
<ABC = 80 degrees.
<x + <ABC = 180
<x + 80 = 180
<x = 100 degrees
Discussion
I cannot be sure what the arc at B is equal to. Is the arc = 80 o or is <ABC = 80. And it is unresolvable. My suggestion is that you ask your teacher.