Answer:
The measure of the arc is 160 degrees
Step-by-step explanation:
The picture of the question in the attached figure
we know that
The measure of the external angle is the semi-difference of the arches it covers.
so
[tex]20^o=\frac{1}{2}[(360-x)^o-x^o][/tex]
solve for x
[tex]40^o=360^o-2x[/tex]
[tex]2x=360^o-40^o\\2x=320^o\\x=160^o[/tex]
