Respuesta :

So you subtract 12 to both sides, and 39 - 12 = 27 so it's x = 27. To test this, you add 12 + 27 which equals 39, just like it's stated in da problem. I hope I helped! :-)
39 - x = 12
x ⇒ ?
39 - 12 = x
39 - 12 = 27
x ⇒ 27

Check:-
39 - x = 12
x ⇒ 27
39 - 27 = 12
Correct!

x ⇒ 27