so basically we want to take out the common term or "factor" it, 20 is in the 5 table right? 5x4=20
so lets apply that to our equation, lets divide each term by 5, x+4 is what you have we cant just make the 5 go away though it is still part of this so your answer is 5(x+4)
i hope that makes sense if it doesnt comment :)