This is the fundamental zero additive rule
x - 0 = x
which means that for the set of real numbers, there exist a number such that if added (or subtracted) from any other will not affect such number.
You would need one because you arent yet to 20 so it takes one tenth for example;
1.7 or 7/10
Thats my guess tho man if it is more complicated than that, SORRRYYYY
8! = 8 x 7 x 6 x 5 x 4 x 3 x 2 = 40320.
