Final answer:
The slope of the vertical line passing through (9, -4) and (9, 11) is undefined because the line does not have any horizontal change, indicating an infinite slope.
Step-by-step explanation:
To find the slope of a line passing through two points, we use the formula:
Slope (m) = (Change in y) / (Change in x) = (y2 - y1) / (x2 - x1)
For the points (9, -4) and (9, 11), both have the same x-coordinate but different y-coordinates. This means the line is vertical. A vertical line does not have a rise over run; instead, it goes straight up or down. Therefore, the slope of a vertical line is undefined.
The correct answer is A. UNDEFINED.