The greatest common factor (GCF) of the expression 4x + 16 is 4.
To find the GCF, we need to identify the largest number or term that divides evenly into both 4x and 16. In this case, both terms have a common factor of 4.
When we divide 4x by 4, we get x, and when we divide 16 by 4, we get 4. Therefore, the GCF of 4x and 16 is 4.
It's important to note that the GCF represents the largest factor that both terms have in common. In this case, the GCF is 4, not 16 or any other number.