Actually Welcome to the Concept of the Profit and loss.
Since, in the comparison for the better buy than the 4 boxes for $3.79 is
Option A.) 6 for $5.75
because all other three are costlier than the their original price,
also, 3.79/4 = $0.94
if, $0.94 * 6 = $5.685
so, $5.685 means,the the buy is better that original price.