Notes

1. You could never buy enough snacks to make a polypeptide
2. Ribosomes don't give out individual amino acids
3. The quarters are then absolutely useless
4. This problem is fundamentally wrong - the whole point of money is that it is the same, no matter what
5. There is no reason why the snacks cannot be polypeptides - it makes just as much sense...

1. It said that many choose to buy multiple snacks, therefore giving the option of not buying more snacks. Amino acids alone cannot do anything; however, one polypeptide alone can be a protein.
2. People are not going to buy enough snacks to make a strand of amino acids. They only buy a couple, which makes sense in making the quaternary structure of a protein.
3. The mRNA goes into the ribosome and out comes a polypeptide, not an amino acid. The quarters could also be part of the code here, sense they all go into the machine at once.
4. It logically makes sense that the code would be the entire mRNA, not just a single codon.
5. Snacks can be mixed together into a blend. However, they cannot be bonded together in any way that would at all resemble peptide bonds.

Basically, though the snacks as amino acids would work, it also makes sense for them to be polypeptides. If you think logically about the problem, even with its flaws, then either way would work.