Answer :

[tex]5x+20=5(x+4)[/tex]
First, find the GCF of 5 and 20. 
The GCF of 5 and 20 is 5.

Second, divide each number by the GCF.
5x/5=x
20/5=4

Finally put the GCF outside the parentheses and the number inside. 
5(x+4)