well just by looking at it, it has to be A
this is why:
we can reason this just by lookinng at it or mathematically
just by looking:
you are buying more chocolate for less money and that is the best buy.
math:
option A) 250 / 4.5 = 55.56 grams of chocolate per dollar
option B) 200 / 6 = 33.33 grams of cholocate per dollar
again for option A you are buying more cholocate.
i hope this helped and have a nice day!