Depending on which rule you apply there are diffrent solutions.
I agree with the rest, that there is one (or more) rule (they probably are essentially the same thing) with which you'll get 30 as answer.
However another rule would get you 60 or 6 and I'm sure you could find many other resonable solutions. Comment if you got how I came to the answer being 60 or 6.

Interesting is that 5 ways I tested I got 30 as answer. So it's probably the best one.