The sum is (n-2)180. N is the number of sides. In this case, you have 20 sides. You get (20-2)180, which is 18x180 and results in 3240 degrees. This is the sum!! To get one angle, do the same thing but divide it by 20. The formula, as seen in the question, is (n-2)180/n. Therefore, you have (20-2) 180 divided by the number of signs, which is 20. Since 18 times 180 = 3240 is the (n-2)180, divide 3240 by 20. You get 162° for each angle.
