For any number $x$, we are told that $x\&=7-x$ and $\&x = x -7$. What is the value of $\&(12\&)$?
We are given two rules for $\&$: one for when it comes after a number, and one for when it comes before a number. To find the value of $\&(12\&)$, we need to apply both rules, but in which order? Well, we can see that the expression $12\&$ has $\&$ after a number, so we can use the first rule to simplify it. According to the first rule, $x\&=7-x$, so we can plug in $x=12$ and get $12\&=7-12=-5$. Now we have $\&(-5)$, which has $\&$ before a number, so we can use the second rule to simplify it. According to the second rule, $\&x=x-7$, so we can plug in $x=-5$ and get $\&(-5)=-5-7=-12$. Therefore, the value of $\&(12\&)$ is -12. 