#### Answer

-12

#### Work Step by Step

Two numbers that are the same distance from 0 but lie on opposite sides of 0 are called opposites of each other.
We know that the opposite of a number $a$ is $-a$, because $a+(-a)=a-a=0$.
Therefore, the opposite of 12 is -12, because $12+(-12)=12-12=0$.