Aregular polygon has possible angles of rotational symmetry of 20°, 40°, and 80°. how many sides does the polygon have?

Angle of rotational symmetry is the angle one can turn a figure and the figure appears unchanged. (learner.org)

Also, any multiple of the least angle of rotational symmetry is also an angle of rotational symmetry.  Thus, 40 and 80 are automatically angles of rotational symmetry if 20 is one.

So the regular polygon must have at least 360/20=18 sides.
note: 36, 54,... sides will also work.  The questions appears to mean to ask for the minimum number of sides of the polygon.

The answer should be 3%