Both -5x and 5 have the factor 5 in common. This means that you can factor out 5:
5(-x + 1)
Generally you don't want the x to be negative when you are factoring so you will factor the negative sign out. This will make the x positive and you will take the opposite of the other value. In this case 1 will become -1
-5(x - 1)
Hope this helped!
~Just a girl in love with Shawn Mendes