Answer
It depends on how much you value the lobster dinner.
Work Step by Step
If you value the entire lobster at more than 80 dollars, then you should stop eating. (Since you value an entire lobster at more than 80 dollars, this is akin to valuing half of a lobster at more than 40 dollars.)
If you value the entire lobster at less than 80 dollars, then you should continue eating. (You have not yet received enough value from the lobster.)
