Answer:
90° counterclockwise or 270° clockwise
Explanation:
The easiest way to visualize this problem is to pick a segment of the quadrilateral and compare it to the corresponding segment on the other quadrilateral. For example, if I pick segment AB, I can compare it to segment A'B' and see that the two lines make a 90 degree angle with other. This means that quadrilateral ABCD can wither be rotated 90° counterclockwise or 270° clockwise.