Answer:
360 degrees
Explanation:
A rotation symmetry angle is an angle with which a figure is rotated and still looks the same as if it wasn't turned.
For example, a square has a minimum angle of rotational symmetry of 90 degrees, because if you turn it by 90 degrees, it still looks exactly the same way.
This rotational symmetry is mostly used with regular shapes.
This quadrilateral is not a regular shape, and there's only one way to have it look exactly like it is now... and it's to do a full turn, of 360 degrees.