Answer :
The factors of 28 are 1, 2, 4, 7, 14, and 28.
The factors of 70 are 1, 2, 5, 7, 10, 14, 35, and 70.
The common factors are 1, 2, 7, and 14. Therefore, the greatest common factor is 14.
The factors of 70 are 1, 2, 5, 7, 10, 14, 35, and 70.
The common factors are 1, 2, 7, and 14. Therefore, the greatest common factor is 14.