verify a-(-b)=a+b for
1.a=21. b=18
2.a=118. b=125

1. 21-(-18) =21+18
Verification :  
       - and - is equal to +
So,
       21+18=21+18
         39=39 


2. 118-(-125)=118+125
Verification:
            - and - is equal to +
So,
       118+125=118+125
              243=243