To find a GCF, find the prime numbers that multiply to equal the number you want.
84 = 2 * 42 = 2 * 2 * 21 = 2 * 2 * 3 * 7
96 = 2 * 48 = 2 * 2 * 24 = 2 * 2 * 2 * 12 = 2 * 2 * 2 * 2 * 6 = 2 * 2 * 2 * 2 * 2 * 3
Then you find the factors that each number (84 and 96) have in common:
2 and 2 2
2 and 2 2
3 and 3 3
So you multiply the respective common factors together:
2 * 2 * 3 = 12
And 12 is your GCF.
