What are the coordinates of vertex B' if the figure is rotated
90° counterclockwise about the origin?

Answer:
Answer: B'(-5,2)
Step-by-step explanation:
Rotations
When rotating a point B(x,y) 90 degrees counterclockwise about the origin it maps to an image point B'(-y,x).
The image shows a figure formed by points ABCD. The coordinates of B are B(2,5).
This point will be rotated 90 degrees counterclockwise about the origin, thus the coordinates of the image point B' are B'(-5,2).
Answer: B'(-5,2)