−A function p => p + 3000 adds a 3,000-won shipping charge to a product price. For an array, we must take each price, add the charge, and put it in a new array; if a price might be absent or a lookup might fail, we must check that first. The calculation is one line, but extracting and repackaging values adds different code for each structure.
+The function p => p + 3000 adds a 3,000-won shipping charge in one line, but applying it to an array means taking out each price, adding the charge, and putting it in a new array; possible absence or a failed lookup calls for another check first. The calculation stays the same while each structure adds its own code for extracting and repackaging the value.
