The greatest common factor: The way I learned it was: I took the number (in this case it's 16 and 36) I took 16 and listed out the numbers that go into 16 like:1, 2, 4, 8, and 16. You would do the same thing for 36. List out the numbers that go into that, and after that, you would find the biggest number that they have in common. I hunk that way is easier than the tree. We actually learned this a week ago, and I got an A+. I hope this helped! Good luck!