The sum of the measures of all exterior angle in a polygon with n sides is always .
Nonagon is a polygon with 9 sides. If this nonagon is regular or equiangular, then all interior angle are congruent, and therefore all exterior angles are congruent. Then the measure of each exterior angle is .
You would need to use the distance formula. Distance = Sqrt((x2-x1)^2+(y2-y1)^2) Plug in your numbers Distance = Sqrt((12+4)^2+(12-18)^2) Distance = 17.09