Here are the answers to your questions:
Question 1:
The greatest common factor can be found by finding the smallest number that is a factor of each number.
Question 2:
What are all the factors of 15?
The answer is 1, 3, 15.
Question 3:
If a number is PRIME, its only factors are itself and...
The answer is 1.
Question 4:
What is the greatest common factor of 6 and 12?
The answer is 6.
Question 5:
What is the greatest common factor of 18 and 24?
The answer is 6.
Feel free to ask if you have more questions!