Answer is 12
Step by step:
Your equation is
N/3 +4 = 8
Subtract 4 from both sides to isolate your variable
N/3 +4 -4 = 8 -4
N/3 = 4
Multiply both sides by 3 to solve for N
N/3 * 3 = 4 * 3 (note, this cancels out the denominator of your variable N)
N = 12