If the numbers are consecutive multiples of 6, and you want to call the smallest one ' n ', then the next one is (n+6) and the biggest one is (n+12).
Their sum is (3n + 18). That's choice-C .
If you run into the same problem again, you might like to call the middle number ' n '. Then the smallest one is (n-6) and the biggest one is (n+6),
and their sum is just 3n ! This is a lot easier to do in your head.
