Answer:
The gcf of 42 and 48 can be obtained like this:
The factors of 42 are 42, 21, 14, 7, 6, 3, 2, 1.
The factors of 48 are 48, 24, 16, 12, 8, 6, 4, 3, 2, 1.
The common factors of 42 and 48 are 6, 3, 2, 1, intersecting the two sets above.
In the intersection factors of 42 ∩ factors of 48 the greatest element is 6.
Therefore, the greatest common factor of 42 and 48 is 6.
Taking the above into account you also know how to find all the common factors of 42 and 48, not just the greatest.
Hope I helped