21) In the given figure : there are 7 equal sides.
A regular heptagon, in which all sides and all angles are equal, has internal angles of 5π/7 radians.
Internal angle : 5π/7 = 128.571°
The sum of all angles on straight line is 180 degree
So, n + 128.57 = 180
n = 180 - 128.57
n = 51.43
Answer : n = 51.43
