You can subtract a negative number from a positive number or add a positive number to a negative number
Example:
4 - (7) = -3
Or
-8 + 9 = 1
Whatever you are adding has to be greater than the number you are adding on too
Example:
-3 + 5 = 2
Notice how the five is greater than 3
Whatever you are subtracting has to be Greater than the number you are subtracting from.
Example:
5 - 8 = -3
Notice how the eight is greater than five.
The situation changed when adding or subtracting with negative numbers. Every situation is different.
Hope this helps!