Answer:
The root word, 'just,' means; equity or fairness.
The prefix that will be added to make the word mean, "not fair" is Un.
Explanation:
Just means fair or lack of impartiality and bias. Agreeing that the judge served justice means that the judge was fair, and objective in his decision.
For the word to mean "not fair," the prefix un would be added to the root word just to give, unjust. When something is unjust, it is not fair. It has elements of bias.
