Let the attendees in opposition be x. This means that the attendees in favour are x+6. That means x+x+6=42, which is 2x+6=42, so 2x=36 and x=18. Therefore, there are 18 attendees who opposed it.
To start off devide both sides by M i.e K/M=LMN/M -> K/M=LN Then devide by K to remove it on the left , this will end you up with M=LN/K So the answer is (c). Hope this helps :).