Final answer:
The rate of change for the music app's pricing is $1.29 per song download, which represents the cost added for each additional song after the initial app purchase.
Step-by-step explanation:
The rate of change in the context of the music app cost refers to the constant amount that the total price increases for each additional song downloaded after the initial download of the app. Since the app itself costs $2 and each song costs $1.29, the rate of change is $1.29 per song download. This rate of change reflects the variable part of the total cost, which is directly proportional to the number of songs downloaded.
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