ABCDEFGHI is a regular polygon with nine sides. What is the measure in degrees of angle ACB?	Choose the correct choice from the following choices:
A) 18  B) 20  C) 25  D) 27  E) 30
the formula of sum of angles in a polygon of sides n=(n-2)*180   so sum of angles=7*180..   therefore each angle ,angle ABC=7*180/9=140..   when we join A and C to make a triangle ABC, it becomes an isosceles triangle with AB and BC equal..   so angle ACB=angleCAB=(180-140)/2=20..   ans 20
<result>B</result>
ABCDEFGHI is a regular polygon with nine sides. What is the measure in degrees of angle ACB?