Answer:
N=4
Explanation:
First, combine like terms: 12=3n
The like terms are 9, -3 and n, 2n which add up to 12=3n
(you add 3 to -3 so it cancels out, then add 3 to the other side of the equation: 9, to get 12)
Second, simply by dividing both sides by 3: 4=N
When you divide 3n by 3 you are left with n, and 12 divided by 3 is 4