What is the greatest common factor for 12 and 30?

Factors of 12: 1, 2, 3, 4, 6, and 12.

Factors of 30: 1, 2, 3, 5, 6, 10, 15, and 30.

Factors common to 12 and 30: 1, 2, 3, and 6.

Greatest factor common to 12 and 30: 6