Choice B is the series of transformations that maps shape A onto shape B. If you know your transformation rules, you can apply them to a single point on your shape to see if they map on to your targeted shape. Here's an explanation:
Using our answer (Choice B) we'll focus on one single point for our transformation rules. Let's use the point (-3,3). Choice B first states that the shape should be reflected across the x-axis, so we'll use the transformation rule (x,-y) which gets us the new point (-3,-3). Next, choice B tells us to reflect the shape over the y-axis, which we can do through the transformation rule (-x,y), which gets us the point (3,-3). Finally, we see that we need to rotate the shape 90 degrees counterclockwise, for which the rule is (-y,x). By doing this we get the final point (3,3). Since this point maps into shape B, this means that all the other points will map onto shape B, making choice B the correct answer.
:)
