What is the GCF of '18' '24' and '42'?

Factors of 18 are: 1, 2, 3, 6, 9, 18
Factors of 24 are: 1, 2, 3, 4, 6, 8, 12, 24
Factors of 42 are: 1, 2, 3, 6, 7, 14, 21, 42

Since 6 is the highest number that will evenly divide into all three numbers, it is the greatest common factor, or GCF.