Answer: You made the mistake of not crossing out the 2 minus signs to make them a plus. 23-(-2) is supposed to become 23+2=25.
Explanation:
23 - (-2)
The first thing to do is remove the parenthesis:
23 - -2
Whenever you have 2 minus signs like - -, you always "cancel" them both (cross them out) and make them a plus sign. Therefore,
23- -2 becomes 23+2
and 23+2= 25
This is why the answer is 25, not 21. In order for it to be 21, the equation would have to be 23 + (-2), because whenever there is a + then a minus, it becomes a -, or means subtraction. So 23+(-2)= 23-2= 21.
Hope this helps!! :D