Honor roll

I made honor roll twice in a row for school. I am hoping to make it again, though I'm very good at Math. I have found a way to improve my math work by checking the answers. How I check the answer's are by either adding or subtracting a number and then to check it, if I added then I would subtract.


Example:


342 -200 =142 then check it by reversing it 200 + 142 =342