Simple...
you have: [tex] \frac{n}{3} =12
[/tex]
and
[tex] \frac{n}{3} =-12[/tex]
To solve for....[tex] \frac{n}{3} =12[/tex]
Multiply to remove the denominator-->>
[tex]3* \frac{n}{3} =12*3[/tex]
n=12*3
n=36
Then-->>>
[tex] \frac{n}{3} =-12[/tex]
Do the same thing-->>
[tex]3* \frac{n}{3} =-12*3[/tex]
n=-12*3
n=-36
Thus, your answer.