I don't really know, but if I had to guess I would say that it would be something like this?
x = x - 5
x - 5 = x
x = x - 5
etc
so like, it would just go on until x = 0
say that the beginning x is 25
20 = 25 - 5
5 - 20 = 15
10 = 15 - 5
etc
i dont know, thats all I got and i hoped this helped even a little bit? im not sure
have a luvly day!