Answer:
23 units
Step-by-step explanation:
The length of a segment that goes from (x1, y1) to (x2, y2) can be calculated as:
So, we can find the length of the segment that goes from (-8, 21) to (-8, -2) replacing (x1, y1) by (-8, 21) and (x2, y2) by (-8, -2).
Therefore, the segment is 23 units long.