What is the greatest common factor of 60 and 168?

The prime factors of 168 are 2, 2, 2, 3 and 7

The prime factors of 60 are 2, 2, 3 and 5

As two 2s and one 3 are common to both sets of factors the Highest Common Factor of both numbers is 2 x 2 x 3 = 12.