There is an inverse relationship between addition and subtraction.

If a math fact is considered, for example 3 + 7 = 10. Then the following are also true:

Similar relationships exist for subtraction, for example 10 - 3 = 7. Then the following are also true:

The reason for this is that we are dealing with an equation. An equation
is balanced or the same on either side of the equals (=) sign. If exactly the
same thing is done to both sides of the equation, it will still be balanced or equal.

In the example above we start with the equation 3 + 7 = 10

- Subtract the same number from both sides 3 + 7 - 3 = 10 - 3
- On the left side the 3 and -3 produce 0 which leaves 7 = 10 - 3
- Turning the equation around to be in more normal form 10 - 3 = 7