Iknow the answer but my teacher told me how and why but i dont know so can some one tell me how and why

there are two sizes of milk to choose from at the grocery store. a 3-quart carton cost $ 2.78 while a 4-quart carton cost 3.87 which is the more economical buy and why

answer choices are

a. the 3quart because its priced at 93 cents a quart
b. the 3quart because its priced at 96 cents a quart
c. the 4quart because its priced at 97 cents a quart
d. the 4quart because its priced at 92 cents a quart