Interesting 'average' question that starts from back to front

[bat18]

I have an interesting average question for you.

I have a number that we will call x

I have 15 random numbers. I want to work out what combination of 12 or more of these numbers will result in an average that is the closest number to x.

I would then like excel to highlight which 12 or more numbers it has used to find the closest average.

Sounds impossible to me so hopefully someone can prove me wrong.

Cheers