a:c=3 rest 1 => a=3c+1
b:c=4 rest 1 => b=4c+1
daca:  a+b+c=82  =>  3c+1  +  4c+1  +  c  = 82
                          8c = 82-1-1
                           c = 10
               => a = 3*10+1 = 31  si  b = 4*10+1 = 41