Answer:
Accordingly, the challenger needs to take 6 balls and divide them equally between the 2 sides of the scale, leaving 2 balls. Two cases can occur:

Case 1: The heaviest ball is among the 6 weighed balls. In this case, we have eliminated 3 balls on the lighter scale, so we only need to take 2 balls from the heavier scale and put them back on both sides of the scale. If the scales are equal, the heaviest ball is the one that is not weighed, if there is a difference, it is on the side with the tilt.

Case 2: The heaviest ball is among the 2 balls that are not weighed, meaning the remaining 6 balls are equal. At this point, we simply need to take these 2 balls and put them on the scale again to determine.