Answer
Absolute value of 31 is 31.
Opposite of 31=-31.
Work Step by Step
Since the absolute value of a number $A$ is that number's distance from 0 on the number line, if $A=31$, then $|31|=31$;
Since the opposite of a number $A$ is to put a negative sign in front of the number, if $A=31, -A=-31$.