the picture in the attached figure
we know that
the sum of the interior angles of a polygon is (n-2)*180
where
n is the number of sides.
For n=9 sides (a nonagon has nine sides)
the sum of the interior angles =(9-2)*180--------> 1260°
Is a regular nonagon
so
each interior angle has the same degrees:
1260/9=140 degrees
x is the exterior angle
exterior angle=180-interior angle-------> 180-140=40°
the answer is
the angle x measure 40°