Explanation:
Think of the problem as x-3 = 2 where x is the blank that we need to fill in.
Adding on -3 is the same as subtracting 3, so that's why x+(-3) is the same as x-3.
To solve x-3 = 2, we add 3 to both sides and we'll get x = 5
Then note how 5-3 = 2 to help confirm the answer.