Can you please answer, my parents are going to be so mad if I can't correct by like the afternoon right now its about 1:31.Anyone know inverse operations, cause I am confused, I looked online and it said Example: 20 + 9 = 29 can be reversed by 29 − 9 = 20 (back to where we started)
And the other way around:

Example: 15 − 3 = 12 can be reversed by 12 + 3 = 15 (back to where we started)
so like when do we do the 2nd way or can we just do either one of them???