Answer:
28
Step-by-step explanation:
The factors of 56 are: 1, 2, 4, 7, 8, 14, 28, 56
The factors of 84 are: 1, 2, 3, 4, 6, 7, 12, 14, 21, 28, 42, 84
The factors of 140 are: 1, 2, 4, 5, 7, 10, 14, 20, 28, 35, 70, 140
Then the greatest common factor is 28.
Hope this helps!