As soon as possible. image provided below of the answer

That would be first option since he did use the inverse of subtraction and added 4.5.

Insha's work is incorrectly because -4.5 + (-4.5) will not cancel each other out. It's supposed to be -9, then she should add 9 to cancel -9 out and she would have gotten 3.

Final A

Hope this is clear.

20000 as first it increases by 2500 then by 5000 so next it will increase by 10000