A single number cannot have a highest common factor because "common" refers to factors that two or more numbers have in common. You have only one number.
You need at least two numbers to find a GCF.
The GCF is 5.
The GCF is 10.
The GCF is 16.
The GCF is 8.
20
4
8
It is 16
It is: 8
It is 16
10
5