36
Step-by-step explanation:
Given that :
Rotation about polygon's center = 20°
To carry the polygon onto itself Angle of rotation is obtained by :
360° / n
Where n is the number of sides in the polygon :
360° / n = 20°
360° = 20 * n
360 = 20n
n = 360 / 20
n = 18
Hence, the polygon has 18 sides or a multiple of 18