How do you subtract a larger number from a smaller number?

When subtracting a larger number from a smaller number you'll end up with a negative number. You subtract to 0 then count from - 1 depending on how much you're subtracting, for ex.

5-6 = - 1

10-20 = - 10

69-100 = 31

I hope this makes sense i tried to explain it in my own words

(a-b) = b-a - (a-b) = b-a.