The answer is 4.
Why?
The prime factorization of 64 is: 2 x 2 x 2 x 2 x 2 x 2. The prime factors and multiplicities 28 and 64 have in common are: 2 x 2. 2 x 2 is the gcf of 28 and 64. gcf(28,64) = 4.
