Question: what is the greatest common factor between 63 and 99?
Answer: The prime factorization of 63 is: 3 x 3 x 7.
The prime factorization of 99 is: 3 x 3 x 11.
The prime factors and multiplicities 63 and 99 have in common are: 3 x 3.
3 x 3 is the gcf of 63 and 99.
gcf(63,99) = 9.