Answer: non-proportional
Explanation:
A proportional pricing method would ensure that the various quantities of milk have the same relative price relating to their quantity. For instance, a half gallon of milk should be half the price of a full gallon of milk for it to be Proportional.
In this example, a gallon costs $3.89. If it were proportional then a half gallon would cost;
= 3.89/2
= $1.95
It instead costs $1.99 which means that it is Non-Proportional.