Hello!
Answer:
![\boxed{C=9}](https://img.qammunity.org/2020/formulas/mathematics/middle-school/atoq148tvg31ojgt1kkw9bwdmonj6bi38l.png)
*The answer must have a POSITIVE sign!*
Explanation:
First, you subtract by 12 from both sides of an equation.
![12-9+c-12=12-12](https://img.qammunity.org/2020/formulas/mathematics/middle-school/v4ltg0avykza97lk2mlh7wl7528vlxw2k2.png)
Simplify by equation.
![-9+c=0](https://img.qammunity.org/2020/formulas/mathematics/middle-school/vheqrxakrrl3q3q816t6aczwnkzjjxwnlj.png)
Then, you add by 9 from both sides of an equation.
![-9+c+9=0+9](https://img.qammunity.org/2020/formulas/mathematics/middle-school/zw28ivqhinlu3o39t66jkrs3j7tm4hpwvp.png)
Add by the numbers from left to right.
![0+9=9](https://img.qammunity.org/2020/formulas/mathematics/middle-school/vdfbeu0rwcdim2v6q0l6tybtz34hjp8658.png)
, which is our final answer.
Hope this helps!
Thanks!
-Charlie
Have a great day! :)
:D