8th grade
posted by andrew .
n+3=12

n=9

Please indicate subject rather than grade level.
Subtract 3 from both sides of the equation to get your answer.
I hope this helps a little more. Thanks for asking. 
n+3=12
n=(4)
4x3=12..... simple :) 
n+3=12
12
 3
_____
9 n+3=12
CHECK IT! 9+3=12
9 n=9
+3
___
12 TADA!!! 
n+3=12
transposing (3)to r.h.s
n=123
n=9 
n=9.

5x8=7