First you need to find on interior angle of a triangle. We know that the polygon has 13 sides and we also know that all of the exterior angles have to add up to 360 degrees. We have to divide the number of sides by 360 360/13=27.69 So one exterior angle is about 27.69 degrees. (If you want to check you can multiply the number of sides by one angle measure to see if it is right) 27.69*13=359.9 Thats about as close as you can get. Hope it helps! :)
