Answer:
5x + 1 = 4x
You can really put any letter for "a number":
5n + 1 = 4n
According to the probles represented above, there is addition of two angles which makes it totally clear. I am pretty sure that the answer with the actual reason of this task is the second option <span>B. Angle Addition Postulate, as you can see a couple of new angles in there :)
Regards!</span>
