One way to find the GCF of 4 and 84 is to compare the prime factorization of each number. To find the prime factorization, you can follow the instructions for each number here:
Here is the prime factorization of 4:
And this is the prime factorization of 84:
When you compare the prime factorization of these two numbers, you can see that there are matching prime factors. You can now find the Greatest Common Factor of 4 and 84 by multiplying all the matching prime factors to get a GCF of 4 and 84 as 4:
Thus, the GCF of 4 and 84 is: 4