Factors of 15 include 3 and 5; multiples of 15 include 30, 45, 60 and more.
In this case, the greatest common factor is 4.
So in general we can say that there are 6 positive and 6 negative common factors of 32.
When we counted the Factors of 27 that we listed above, we found that 27 has 4 Positive Factors and 4 Negative Factors.
You might not always realize basic maths principles when you use them in real life, just as you probably don't notice the alphabet every time you read.
In constructing the tree, be sure to remember the second item in a factor pair.