A nonagon has nine sides.
The sum of the measures of the interior angles of a polygon is (n-2)*180 where n is the number of sides. In this case it's (9-2)*180 = 7*180 = 1260
This nonagon is equiangular, which means all the angles are equal. That means each angle measures total/#angles = 1260/9 = 140 degrees.
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