Answer:
b: a rotation of 90° about B
Explanation:
A transformation down and right of the figure look like this:
Where the figure is just translated, so the orientation of the figure is the same.
In the same way, a rotation of 360° doesn't change the figure, because it is equivalent to make a full turn of the figure.
Finally, a rotation of 90° about B looks like this:
Where each segment of the initial figure forms an angle of 90° with its corresponding segment of the reflected figure. For example, BA is perpendicular to B'A'
Therefore, the answer is b: a rotation of 90° about B.
