Only rectangle and square are the polygons in which measure of an exterior angle at the vertex of a polygon equals the measure of the adjacent interior angle because each has angle is right angle.
such that the exterior angle = 180°-90°=90°
Rest of the polygons does not satisfy the statement that the measure of an exterior angle at the vertex of a polygon equals the measure of the adjacent interior angle.
Since in equilateral triangle each angle is of 60°, that is the measure of exterior angle = 180°-60°=120°