To rotate a point \( (x, y) \) counterclockwise by 90 degrees about the origin, the mapping rule is:
\[ (x, y) \rightarrow (-y, x) \]
For the point \( W(-3, 7) \):
- Apply the rule: \[ W' = (-7, -3) \]
So the coordinates of \( W' \) after a 90-degree counterclockwise rotation about the origin are:
\[ W'(-7, -3) \]