To determine the price of 4 gallons of organic milk when the price is given per half gallon, you should first find out how many half gallons are in 4 gallons.
1 gallon equals 2 half gallons, so 4 gallons is equal to \(4 \times 2 = 8\) half gallons.
Now, since the cost of one half gallon is $2.52, the total cost for 8 half gallons can be found by multiplying the price of one half gallon by the number of half gallons:
\[ \text{Total Cost} = 2.52 \times 8 \]
Thus, the correct method is to find the unit price and multiply it by 8 (the number of half gallons in 4 gallons).
Therefore, the answer is: by finding the unit price and multiplying it by 8 (but since the options provided don’t mention multiplying by 8, the closest correct method would involve calculating based on half gallons). If "finding the unit price and multiplying it by 4" is defined as considering 4 half gallons (which is incorrect for our case), it would systematically be incorrect as well.
None of the provided options give the correct procedure explicitly since they do not account for the total number of half gallons for 4 gallons. However, the concept of conversion should drive the multiplication to be based on half gallons in this context. If strictly between available options for 4 half gallons: by finding the unit price and multiplying it by 4 is mathematically misplaced but comes closer, albeit dislocated for larger quantity-driven contexts.