If the requirement is taste and or nutrition there are a few ways you could do this.

1) From a caloric perspective. Work out how many calories are need for the average person in the average meal. Scale a common McDonalds hamburger to this caloric content then measure the meat
2) From a taste perspective you could arrange a diverse set of taste testing and perform A/B tests to find the optimal hamburger
3) The easiest way is to assume MacDonalds, the largest burger company has already done this, then look on their product information labels to infer the amount of meat.
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