Okay, so it basically means you're subtracting.
I'm going to give some examples of what the answer could be.
1. 5 - 5 = 0
2. 5 - 4 = 1
3. 5 - 3 = 2
4. 5 - 2 = 3
5. 5 - 1 = 4
6. 5 - 0 = 5
Or of course if you feel you would like to switch the order of the problems, go ahead and try that, but no matter what happens, make sure the addition version always equal 5, so just be careful :)