Answer:
x=3
Step-by-step explanation:
You take 12-9 to get 3 :)
[tex]3[/tex]
Simple, all you have to do is backwards equation. If the sum is 12. Subtract 12 by one of the numbers given.
[tex]12 - 9[/tex]
[tex]==> 3[/tex]
[tex]3 + 9 = 12[/tex]
