Answer:
5
Explanation:
In order to find the GCF (Greatest Common Factor) of two numbers, list each number's factors. The number of greatest value that shows in both sets is the GCF.
First, list the factors of 5 and 15.
5 - 1, 5
15 - 1, 3, 5, 15
The numbers that show in both sets are 1 and 5. Since 5 is the greatest of the duplicate numbers, 5 is the GCF.