I really need help pls

First, find the prime factorization of each number.

12/2 = 6
6/2 = 3
3/3 = 1

12 = 2 * 2 * 3 = 2^2 * 3

72/2 = 36
36/2 = 18
18/2 = 9
9/3 = 3
3/3 = 1

72 = 2 * 2 * 2 * 3 * 3 = 2^3 * 3^2

The GCF of two numbers is the product of some of its prime factors.
The prime factors you choose are the common factors with the smaller exponent.

Both 12 and 72 have factor 2. There is a 2^2 and a 2^3.
Choose 2^2, since that has the smaller exponent.

Both 12 and 72 have factor 3. There is a 3 and a 3^2.
Choose 3 since that has the smaller exponent.

The factors you need are 2^2 and 3

GCF = 2^2 * 3 = 4 * 3 = 12