Answer: 4
===========================================
Step-by-step explanation:
For now, ignore the variables. Let's just focus on the coefficients 12 and 16.
The GCF of 12 and 16 is 4 because this is the largest factor they have in common.
12 = 4*3
16 = 4*4
You could create a factor tree to get the prime factorization of each number
12 = 2*2*3
16 = 2*2*2*2
Each factor tree has two copies of '2' leading to the GCF 2*2 = 4.
--------
Now let's go back to the variables. The term 12n and 16w^3 do not have any variables in common. So the final answer won't have any variables in it. If both terms had say a 'w' in them, then w would somehow be involved in the GCF. But that's not the case here. So we just stick to 4 as our answer.
--------
Side note: If you had 12n+16w^3 and you wanted to factor, then you would factor out the GCF 4 to get 12n+16w^3 = 4(3n+4w^3). Use the distribution rule to confirm this.