Answer:
28
Step-by-step explanation:
Any whole number can be broken down into its prime factorization, a product of all the prime number factors of a number. We can use a diagram called a factor tree to break numbers down into those factors. I've attached an image with the factor trees of 84 and 56 so you can see this process; 84 breaks down into 2 × 2 × 3 × 7, and 56 is 2 × 2 × 2 × 7. We can find the greatest common factor of these numbers by collecting all the prime factors they have in common and multiplying them together. 84 and 56 have 2, 2, and 7 in common, so their greatest common factor is 2 × 2 × 7 = 28
