9 = 3 x 3

18 = 3 x 3 x 2

42 = 6 x 7 (which can be broken down into 3 x 2 x 7

So, the GCF of 9, 18, and 42 is 3.

18 = 3 x 3 x 2

42 = 6 x 7 (which can be broken down into 3 x 2 x 7

So, the GCF of 9, 18, and 42 is 3.