The question asks to determine the coordinates of point B' after a 90° rotation. The original coordinates of point B are (4, 2).

For a 90° rotation counterclockwise around the origin, the rule is: $(x, y) \rightarrow (-y, x)$

So, applying this rule to point B(4, 2): $(4, 2) \rightarrow (-2, 4)$

Thus, the coordinates of B' are $(-2, 4)$.

The correct answer is B'(-2, 4).

Would you like more details on rotations, or do you have any questions?

Here are 5 follow-up questions to expand on this concept:

1. What would the coordinates of point C(3, 4) be after a 90° counterclockwise rotation?
2. How do the coordinates change for a 180° rotation?
3. What are the rules for rotating a point 270° counterclockwise?
4. What happens to a point's coordinates if rotated clockwise instead of counterclockwise?
5. How can we generalize the formula for rotating a point about an arbitrary center?

Tip: Always remember to check the direction of rotation (clockwise or counterclockwise) when applying rotation rules!