Answer:
A regular polygon is a polygon that is equilateral and equiangular.
The only regular quadrilateral is the square.
We know that all the interior angles of a square are 90° each, so we are fine with that.
Now, for the exterior angles.
If we fix our position in the vertex, we can do from one side, to the same side, a full rotation of 360°.
Now, if we only do an external rotation, this means, from one side to other side, we will do a rotation of 360° minus the interior angle:
this is:
360° - 90° = 270°
Below is an image as a guide of this.
