Certaincy equivalent meaning. a decisions question

OK.

A friend gambled with my money/ Taking unneeded risk. AgAINST my instructions.

I calculated that I would have took this gamble for an Ev of $10,000.

Now how much does my friend owe me?

10000 or half of this?

I remembern vaguely that the optimal bet size means that the ev is twice the CE of the variance of the bet. Is that true?

Or to the bottom line. I would have gambled thus for 10K. How much is my irresponsible friend owing me mathematically

PS. He agreed to pay what the formula dictates..........

Happy new year