Hello there!
First, let's establish what the greatest common factor means.
The greatest common factor is the highest factor in value that's in comparison to all numbers.
For example;
2, 4, and 8. Find the GCF.
2 = 1 x 2
4 = 1 x 4, 2 x 2
8 = 1 x 8, 2 x 4
These numbers all have 2 as the highest number in common, so 2 is the GCF in this example.
Now, let's try with our current numbers.
30 = 1 x 30, 3 x 10, 5 x 6
48 = 1 x 48, 2 x 24, 3 x 16, 4 x 12, 6 x 8
60 = 1 x 60, 2 x 30, 3 x 20, 4 x 15, 5 x 12, 6 x 10
All of our numbers have these common factors:
1, 2, 3, 5, 6.
The greatest number is 6, so our GCF is 6.
I hope this helps!
