First, let's define 'Greatest Common Factor'
The Greatest Common Factor also known as GCF is the largest number that can divide equally into two or more numbers.
For the problem they ask 'Which number pair has a 'GCF' of 6.
First let's look at the answer choice 'A' that gives us 18 and 54.
Now for this we need to list the factors of both 18 and 54. A factor being a number that can be multiplied by another number to get the sum.
18: 1, 2, 3, 6, 9, 18
54: 1, 2, 3, 6, 9, 18, 27, 54
So right away we can see the the largest number that can be divided into both of them equally is not 6, it is 18. This means we can mark out A as a possible answer.
Next let's try B and list the factors of both 30 and 42.
30: 1, 2, 3, 5, 6, 15, 30
42: 1, 2, 3, 6, 7, 14, 21, 42
Looks like we found our answer! The largest factor they have in common is 6!
I'm still going to go ahead and list the GCF's for answers C and D.
C. 30, 60
30: 1, 2, 3, 5, 6, 15, 30
60: 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30, 60
GCF for answer choice C = 30
D. 36, 60
36: 1, 2, 3, 4, 6, 9, 12, 18, 36
60: 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30, 60
Final answer: B. 30, 42